enggis_v&r

7/24/2019 ENGgis_V&R

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Geographic Information Systems(GIS)

tel: 03-4227151-57624

fax: 03-4254908

e-mail: [email protected]

Chi-Farn ChenCSRSR NCU


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Vector and Raster Data Model


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Model and GIS

representation of reality model

GIS itself is based on a model of complexity GIS is used to model complexity

full representation of reality?

Data model =

limited representation of reality


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Data Model

Reality is too complex for even the most

sophisticated GIS software, so in order torepresent reality in a spatial database, a

simplification of reality is created. This

simplification is known as a data model.

In a data model, reality is represented by

geometry and attributes.


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There are two formats used by GIS

systems to store and retrieve spatial

data:

Vector

Raster

GIS Data Formats

RasterVector


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Vector Format Data are associated with points, lines, or areas

Points are located by coordinates

Lines are described by a series of points join-the-dots-books

(Arcs nodes, vertices) Areas are described by a series of lines enclosing

the area.

(Polygons)


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Vector Format Any attributes (name or code) can be associated

with a point, line or polygon.

Data are stored in two files:

a file containing information of coordinates a file containing information of the attributes

A third file contains information needed to link

positional data with their attributes (Identifier).


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Coordinates Table

Point ID x y

1 1 3

2 2 1

3 4 14 1 2

5 3 2

1

2 3

4

5

X

Y

common identifiers provide link to:

coordinates table (for where)

attributes table (for what)

Attributes Table

Point ID model year

1 a 90

2 b 90

3 b 804 a 70

5 c 70

Features have unique identifiers:

point ID, line ID, polygon ID


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Raster Format Data are divided into cell, pixels (picture elements)

Pixels are organized in arrays

Row and Column Numbers (coordinates) are used

to identify the location of the pixel within the

array.

Each pixel has a single value (attribute)


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row

pixel:Coordinate: (2,9)

Attribute: 8

column

8

Raster Format


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Vector and Raster Representation ofPoint Map Features

Map FeatureGIS Vector

Format

GIS Raster

Format

(X,Y)

Coordinate in space Pixel Locatedin an Array


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Vector and Raster Representation ofLine Map Features


FormatGIS Raster

Format


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Vector and Raster Representation ofArea Map Features


Format

GIS Raster

Format


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Vector Model

Vector model uses discrete points, lines and/or areas

corresponding to discrete objects with name or code

number of attributes.

Raster Model

Raster model uses regularly spaced grid cells in specific

sequence. An element of the grid cell is called a pixel

(picture element). The conventional sequence is row by row

from the top to bottom and then column by column from

the left to the right. Every location is given in two

dimensional image coordinates; row number and column

number, which contains a single value of attributes.


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Comparison of Raster and Vector Formats

Raster formats are efficientwhen comparing informationamong arrays with the samecell size.

Raster files are generallyvery large because each celloccupies a separate line ofdata, only one attribute can

be assigned to each cell, andcell sizes are relatively small.

Raster representations arerelatively coarse and

imprecise.

Vector formats are efficientwhen comparing informationwhose geographical shapesand sizes are different.

Vector files are muchsmaller because a relativelysmall number of vectors canprecisely describe large areas

and many attributes can bedescribed to these areas.

Vector representations ofshapes can be very precise.

RasterVector


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Vector Model


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There are different models to store and managevector information. Each of them has different

advantages and disadvantages.

Vector Model

Spaghetti Model (list of coordinates)

Vertex Dictionary Model

Topological Model (Dual Independent Map Encoding: DIME)

Arc / Node Model


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Vector representation without model


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Spaghetti Model (List of coordinates)

simple and easy to manage

lots of duplication, hence need for large storage space

very often used in CAC (computer assisted cartography) no topology


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No Topology


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Spaghetti data often contains

crossing lines, loose ends,double digitization of

common boundaries (slivers) Its a mess!


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Sliver Polygons

Sliver polygons are small, narrow polygonfeatures that inevitably appear along

borders of polygons following the overlay of

two or more geographic data sets.

Often occur when a shared boundary arc is

digitized twice. Should be removed, but difficult to find.


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Sliver Polygons


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Vertex Dictionary Model

no duplication, but still this model does not use topology


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Topological Model (DIME) / (TIGER)

assigns a directional code in the form of a

"from node" and a "to node nodes (intersections of lines) are identified

with codes

developed by US Bureau of the Census

both street addresses and UTM coordinatesare explicitly defined for each link


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Topology


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The GIS vector data model is slightly more complexas each vertex, arc, node and polygon is uniquely

identified and the relationships between them are

stored in the database The relationships betweenthe elements of a vector data model, in terms of

relative location and connections, are known as

Topology. Topology gives the vector data model alevel of intelligence which means that the GIS can

recognize which arcs are joined to each other, and

identify those polygons which are adjacent to each

other.


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Topology:

A GIS topology is a set of rules and behaviors

that model how points, lines, polygons share

geometry. For example, adjacent features,

such as two countries, share a common edge.

Simple definition:

Topology stores the relationships of one

spatial element with respect to another.


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Topology:

Topology is a mathematical approach that

allows us to structure data based on theprinciples of feature adjacency and feature

connectivity.

It is in fact the mathematical method used todefine spatial relationships. Without a

topologic data structure in a vector based GIS

most data manipulation and analysis

functions would not be practical or feasible.


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Defining Topology

Topology :

the spatial relationships between features in a GIS

Do polygons overlap?

Do lines intersect or connect?Are points located near each other?


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Topology:

Three main concepts

Connectivity Arc-node topology

Definition of areas / Containment Polygon-arc topology

Adjacency/Contiguity

Left/right topology


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Topology : spatial relationship

Connectivity:

The topological identification of connected arcs by recording the from- and to-node

for each arc. Arcs that share a common node are connected.

Arcs connect to each other at nodes

Describing linear network, links have direction.

Area:

Arcs that connect to surround an area define a polygon

Containment:Accounts for polygons within polygons islands

Describing which landscape features are located within, or intersect, the boundary of

polygons

Adjacency:The identification of adjacent polygons by recording the left-hand and right-hand

polygons.

Arcs have direction and left and right sides

Describing a landscape features neighbor


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Concept of Topology

Topology distinguishes GIS data models from non-

topological data models supported by many CAD, mapping

and graphics systems

Topology refers to knowledge about relative spatial

positioning of features.

knowledge about how features are connected and which features

are adjacent to each other.

Can be viewed as a mathematical procedure that

determines spatial properties and relationships, including:

Connectivity, contiguity (adjacency)

Lengths of arcs and areas of polygons


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Topology Rules for Coverages:

Each arc has a beginning node and an ending

node - this determines directionality.

Directionality is determined during digitizing.

Actual direction is important only if your

application requires directional modeling.

Arcs connect to other arcs at nodes Connected arcs form polygon boundaries - arc

coordinates are stored only once because two

adjacent polygons share the common arcbetween them.

Arcs have polygons on their left and right sides


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Topology Concept I

Arc-node topology is how Arc/INFO keeps trackof which arcs are connected to other arcs through

shared nodes (nodes are endpoints of arcs). It

defines length, direction, and connectivity for arcs.

The from-node is an arcs starting point; the to-node

is its ending point. They are determined as you

digitize your data. You can see the from-node and

to-node whenever you list attribute records for a

coverage containing lines. Arcs connect if they

share a node.


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Topology Concept II

Polygon-arc topology expresses the relationshipbetween the arc features and the polygon features

for which the arcs create boundaries. It defines

area and adjacency. Arcs or a set of arcs that form

a closed figure define the area of a polygon. Two

polygons are adjacent if they share an arc. Polygonsare stored as a list of arcs to avoid redundancy.


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Topology Concept III

Left-right topology refers to contiguity -- howpolygons are associated with their neighboring

polygons. Each arc has a list of which polygons are

on the right side and which are on the left side.Commands in Arc/INFO use this information to

determine from one polygon what the adjacent

polygons are: 1

2

3

4

5

6

7


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Vector Data Model

Points: represent discrete point features

each point locationhas a record in the

table

airports are point features

each point is stored as acoordinate pair


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Lines: represent linear features

roads are linear features

each road segmenthas a record in the

table

Vector Data Model


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Vector Data Model

Lines: fundamental spatial data model

Lines start and end at nodes line #1 goes from node #2 to node #1

Vertices determine shape of line

Nodes and vertices are stored as coordinate pairs_

node

node

vertex

vertex

vertex

vertex


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Vector Data Model

Polygons: represent bounded areas

each bounded polygonhas a record in the

table

landforms and water are

polygonal features


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Polygon #2 is bounded by lines 1 & 2

Line 2 has polygon 1 on left and polygon 2 on right_

Polygons: fundamental spatial data model

Vector Data Model


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complex data model, especially for larger data sets

arc-node topology, only used for ArcInfo data sets_

Polygons: fundamental spatial data model

Vector Data Model


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Connectivity

Arc-node topology


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Definition of areas

Polygon-arc topology


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Adjacency/Contiguity

Left/right topology


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Arc / Node Model


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File 1. Coordinates of nodes and vertex for all the arcs

ARC F_node Vertex T_node

1 3.2, 5.2 1, 5.2 1,3

2 1,3 1.8,2.6 2.8,3 3.3,4 3.2, 5.2

3 1,2 3.5,2 4.2,2.7 5.2,2.7

File 2. Arcs topology

ARC F_node T_node R_poly L_poly

1 1 2 External A

2 2 1 A External

3 3 4 External External

File 3. Polygons topology

Polygon Arcs

A 1, 2

File 4. Nodes topology

Node Arcs

1 1,2

2 1,2

3 3

4 4

Arc / Node Model

G f


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The geometry of a point is given by two dimensionalcoordinates (x, y), while line, string and area are given

by a series of point coordinates.

The topology however defines additional structure as follows

Node : an intersect of more than two lines or strings, or start

and end point of string with node number

Arc : a line or a string with chain number, start and end

node number, left and right neighbored polygons

Polygon : an area with polygon number, series of arcs thatform the area in clockwise order (minus sign is

assigned in case of anti-clockwise order).

Geometry and Topology of Vector Data


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Area-Area Relationships"overlaps" : two areas overlap

"is within" : an island within an area"is adjacent to" : two area share a common boudary

Topological Relationships between Spatial Objects

Point-Pont Relationship"is within" : within a certain distance"is nearest to" : nearest to a certain point

Point-Line Relationships"on line" : point on a line"is nearest to" : a point nearest to a linePoint-area Relationships"is contained in? : a point in an area"on border of area" : a point on border of an area

Line-Line Relationships"intersects" : two lines intersect"crosses" : two lines cross without an intersect"flow into" : a stream flows into the river

Line-Area Relationship"intersects" : a line intersects an area"borders" : a line is a part of border of an area


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Topology Review

Topology is the spatial relationship betweenconnecting or adjacent features in a geographicdata layer.

A procedure used by the computer to explicitly defineand store the spatial relationships between connecting

or adjacent coverage features.

Think of topology as geometry on a rubber sheet. This type of geometry is concerned with spatial

relationships rather than ridged coordinate location.


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Topology Review

If a map is stretched and distorted, some

properties change: Distances

Angles

Relative proximities


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Topology Review

Other properties (topological properties) remain

constant after distortion: Adjacency

Containment

Connectivity

Areas remain areas, lines remain lines, points

remain points


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Topology Review

By tracking all the arcs that meet at any node,

topology knows which arcs connect to each other.

(Arc-node topology) A list of arcs is used to construct the polygon.

Storing each arc only once reduces the amount of

data and ensures that the boundaries of adjacentpolygons do not overlap.

(Polygon-arc topology)

It is easy to find the similar characteristic between

adjacent polygons.

(Left-right topology)


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Vector Topology helps deal with:

overshoots

slivers

dangles

Not sharing border

Topology Review


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Bureau of the census

Address matching to convert street addresses to

geographic coordinates and census reporting zones

With geographic coordinates, data could beaggregated to user-specified custom reporting zones

DIME files were the major component of thegeocoding approach

TIGER


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Address Matching or Geocoding:A list of addresses is converted to

points on a map by referencing themto a special street network.

Address Matching


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TIGER Address Range Example


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Two input files and one output file

Input:A database (dbf) file that has the address list that

needs to be geocoded.

A geographic base file or reference layer (commonlystreet layer) that will spatially reference the address

location with the address database (input1).

Output:This will be a point file that will hold the geocoded

address locations with an attribute file that shows the

full address and the matching accuracy.

Address Matching or Geocoding:

Address Matching

?


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Tabular dataText

Databases

to

Geographic maps

TIGER Streets

ZIP Codes

What do you match?


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Raster Model

Raster Model


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A raster data model uses a

grid.

One grid cell is one unit orholds one attribute.

Every cell has a value, even if

it is missing. A cell can hold a number or

an index value standing for an

attribute. A cell has a resolution, given

as the cell size in ground units.

Raster Model

Raster Data Structures


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Raster Data Structures

Square grid: equal length sides

conceptually simplest

cells can be recursively divided into

cells of same shape

4-connected neighborhood (above,below, left, right)

all neighboring cells are

equidistant

8-connected neighborhood (alsoinclude diagonals)

all neighboring cells not

equidistant

center of cells on diagonal is 1.41units away (square root of 2)

rectangular

commonly occurs for lat/long

when projected

data collected at 1degree by 1

degree will be varying sizedrectangles

triangular (3-sided) and

hexagonal (6-sided)

all adjacent cells and points areequidistant

triangulated irregular

network (tin):

vector model used to represent

continuous surfaces (elevation) more later under vector


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Resolution(pixel size)

column

row pixel:Coordinate: (2,9)Attribute: 3

Raster Model (Grid, Image)

choose raster pixel size 1/2 the length (1/4 the area)

of smallest feature to map (smallest feature called

minimum mapping unit or resel--resolution element)

A i t hAssignment scheme


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The value of a cell may be:The value of a cell may be:

an average over the cellan average over the cell a total within the cella total within the cell

max or min or the commonest value in the cellmax or min or the commonest value in the cell

tthe value found at the cellhe value found at the cells central points central point

Assignment schemeAssignment scheme



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Line assignment Polygon assignment


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The mixed pixel problem

W GWW W G

W W G

W GGW W G

W G G

W GEW E G

E E G

Water dominates Winner takes all Edges separate

R D


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Each cell can be owned by only one feature.

Raster is easy to understand, easy to read and

write, and easy to draw on the screen. Spatial analytical operations are faster

Grids are poor at representing points, lines and

areas, but good at surfaces.Grids are a natural representation for scanned

or remotely sensed data.

Grids suffer from the mixed pixel problem.Grid compression is easier

techniques used in

GIS are run-length encoding and quad trees).

Raster Data


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Raster Data Sources

Scanned maps

B & W aerial photos

Color aerial photos

Satellite images

Run Length Encoded Compression


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Run-Length Encoded Compression

Uncompressed:

AAADDDDDDBBBBBBBBBCCCCDDDD

DBBBBBAAAA

Run-Length Encoded:

3A6D9B4C5D5B4A

A A A D D D

D D D B B B

B B B B B B

C C C C D D

D D D B B B

B B A A A A

Data Compression


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Runlength Compression (for single layer)

Full Matrix--162 bytes111111122222222223

111111122222222233

111111122222222333111111222222223333

111113333333333333

111113333333333333111113333333333333

111333333333333333

111333333333333333

1,7,2,17,3,18

1,7,2,16,3,18

1,7,2,15,3,181,6,2,14,3,18

1,5,3,18

1,5,3,181,5,3,18

1,3,3,18

1,3,3,18

Run Length (row)--44 bytes

Value thru column coding.

1st number is value, 2nd islast column with that value.

Now, GIS packages generally rely on commercial

compression routines. Pkzip is the most common, general

purpose routine. MrSid (from Lizard Technology)and

ECW (from ER Mapper) are used for images. All these

essentially use the same concept. Occasionally, data is still

delivered to you in run-length compression, especially in

remote sensing applications.

This is a lossless

compression, asopposed to lossy,

since the original

data can be exactly

reproduced.

Basic Quadtree Compression


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Basic Quadtree Compression

G = Gray W = White

Quadtree Compression:G0,G10,G11,G12,W13,G200,G201,G210,G211,W202,W203,W212,W213,W22,W23,W3

NOTE: There are many variations of the quadtree compression.The one above represents one of the most basic.

0 1

2 3

0 1

2 3

11

12 13

10

201

202 203

200 211

212 213

210

22 23

Basic QuadtreeStructure 0 1

2 3

11

12 13

10

201

202 203

200 211

212 213

210

22 23

Data Compression


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Data CompressionQuad Tree Representation (for single layer)

sides of square grid divided evenlyon a recursive basis

length decreases by half # of areas increases fourfold

area decreases by one fourth

Resample by combining (e.g.

average) the four cell values although storage increases if save allsamples, can save processing costs ifsome operations dont need highresolution

for nominal or binary data can savestorage by usingmaximum block

representation

all blocks with same value at any one

level in tree can be stored as singlevalue

Layer Width Cell

Count

1 1 12 2 4

3 4 16

4 8 64

5 16 2566 32 1024

store this quadrant

as single 1

store this quadrant

as single zero

1 11 1

1 1

1

1

I 1,0,1,1 II 1III 0,0,0,1 IV 0

Essentially involves compression applied to both row and column.

2

2

1

2

3

4

4

4

4

54

4

4

3

4

2

3 4

2.53.5

3.25

Raster Array Representations for multiple layers


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Raster Array Representations for multiple layers

How organize into a one

dimensional data stream for

computer storage & processing?

Band Sequential (BSQ)

each characteristic in a separate file

elevation file, temperature file, etc.

good for compression

good if focus on one characteristic

bad if focus on one area Band Interleaved by Pixel (BIP)

all measurements for a pixel grouped together

good if focus on multiple characteristics of

geographical area

bad if want to remove or add a layer

Band Interleaved by Line (BIL)

rows follow each other for each characteristic

A B

B B

III IV

I II 150 160

120 140Elevation

Soil

Veg

File 1: Veg A,B,B,BFile 2: Soil I,II,III,IV

File 3: El. 120,140,150,160

A,I,120, B,II,140 B,III,150 B,IV,160

A,B,I,II,120,140 B,B,III,IV,150,160

Note that we start in lower left.

Upper left is alternative.


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Fil F t f V t S ti l D t


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Arc Export

Arc Export is a transfer format, either ASCII or

compressed into binary, used to transfer files between

different versions of ARC/INFO. It is undocumented and

will work only with ESRI products.

ARC/INFO Coverages

An ARC/INFO "coverage" is a set of internal binary files

used by ARC/INFO, a GIS program. This file format is

proprietary and not readily usable by other programs.

File Formats for Vector Spatial Data



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ArcView Shape

The shapefile format defines the geometry and attributes ofgeographically-referenced features in as many with specific

file extensions that must be stored in the same projectworkspace. They are:

.shp - the file that stores the feature geometry. (required)

.shx - the file that stores the index of the featuregeometry. (required)

.dbf - the dBASE file that stores the attributeinformation of features. (required)

.sbn and .sbx - the files that store the spatial index of thefeatures. (optional)

ARC/INFO A Vi


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ARC/INFO vs. ArcView

ARC/INFO is a topologically based hybrid system

ArcView is a file based, non topological, pseudoobject-oriented graphic data structure



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ArcGIS has a well-defined model for working with data. This

generic model, called the geodatabase (short for geographicdatabase), defines all the types of data that can be used in

ArcGISfor example, features, rasters, addresses, and

survey measurementsand how they are represented,accessed, stored, managed and processed. The geodatabase is

a common framework shared by all ArcGIS products and

applications.

ArcGIS Geodatabase




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The geodatabase offers you the ability to

Handle rich data types.

Apply sophisticated rules and relationships.

Access large volumes of geographic data stored in both files

and databases.

ArcGIS Geodatabase




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ArcGIS supports a collection of files in a file system or a

collection of tables in a relational database management

system (RDBMS).

Such as several well-known data set types such as

coverages, shapefiles, grids, images, and triangulated

irregular networks (TINs).

And manages the same types of geographic information in

an RDBMS such as DB2, Informix, Oracle, SQL Server,or Microsoft Access.

ArcGIS Geodatabase




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Geodatabase Data Management

Two categories:

Personal Geodatabase Single user editing

Stored in MS Access

Size limit of 2 GB

ArcSDE Geodatabase Enterprise

Supports multiuser editing via

versioning

Requires ArcEditor or ArcInfo Editorto edit



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Comparison of the file and geodatabase implementations

File-Based Data Sets

Coverages

Shapefiles

Grids

TINs

Images

Vector Product Format files

Computer-aided design files

Geography markup language

Tables

XML

DB2 with its Spatial type

Informix with its Spatial type

SQL Server

Oracle

Oracle with Spatial or Locator

Personal geodatabases (Microsoft

Access)

Geodatabase



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AutoCAD" Drawing Files (DWG)

DWG is the internal, proprietary format used in AutoCAD

software, which is a computer-aided design/drafting (CAD)program. Despite its proprietary nature, AutoCAD canconvert any DWG file to a DXF file (described below)without loss of graphic information. As with DXF files,there are a number of ways to store attribute informationin DWG files. The emerging standard is one that usesExtended Entity Data (EED) to link attributes, but many

others are possible. However, the lack of one standard forlinking attributes can cause problems when data istransferred between systems.




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Autodesk's Data Interchange File (DXF) Format

DXF is probably the most widely used vector datatransfer format, and a file in DXF format offers somevery strong advantages. It contains very completedisplay information, and almost every graphics

program can read it. However, there are severaldifferent ways to store attribute information in DXFand to link DXF entities to external attributes. Becausethere are no attribute standards, many programs thatclaim to read DXF files still do not import attributeinformation properly.




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Digital Line Graphs (DLG)

DLG, a transfer format used by the US GeologicalSurvey (USGS), depicts vector information portrayedon printed paper maps. It carries very accuratecoordinate information and sophisticated, feature-

classification information but no other attribute data.DLG does not include any display information. TheDLG standard is significant because the USGS andother US government agencies have used it to publishlarge numbers of digital maps.




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MapInfo" Data Transfer Files (MIF/MID)

MIF/MID is a transfer standard used by MapInfo, a

desktop mapping system. It carries all three types of GISinformation: geographic, attribute, and display. Attribute

links are implicit in the file format.

MapInfo Map Files.

MapInfo has its own internal binary format, known as a

map file. It is undocumented and proprietary, so it cannotbe used outside a MapInfo system.




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MicroStation Design Files (DGN)

DGN is the internal format used by Bentley Systems

Inc.'s MicroStation, a CAD program. It is welldocumented and standardized, so it may also be used asa transfer standard. DGN files contain detailed displayinformation. The most common way to store attributesis to place them in an external database file and recordlinks in the MSLINK field-a data item carried for eachelement in the DGN file.


File Formats for Raster Spatial Data


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File Formats for Raster Spatial Data

The generic raster data model is actually implemented in several different

computer file formats:

GRID is ESRIs proprietary format for storing and processing raster data

Standard industry formats for image data such as JPEG, TIFF and MrSidformats can be used to display raster data, but not for analysis (must

convert to GRID)

Georeferencing information required to display images with mapped

vector data

Requires an accompanying world file which provides locational

information

Image Image File World File

TIFF image.tif image.tfw

Bitmap image.bmp image.bpw

BIL image.bil image.blw

JPEG image.jpg image.jpw

Viewing File


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Viewing File

Most importantly, file information includes organizing it so

that people can logically use it without having to know

anything about itsphysical structure. The difference between logical andphysical:

LOGICAL VIEWLOGICAL VIEW

Focus on how you need to arrange and access informationto meet your particular needs.

PHYSICAL VIEWPHYSICAL VIEW

Deal with how information is physically arranged, stored,

and accessed on some type of secondary storage device.

Logical View and Physical View (Vector Data)


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Logical View - Shape fi le (*.shp)



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Physical View - Shape fi le (*.shp)

Logical View and Physical View (Raster Data)


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Logical View - Imagine fi le (*.img)



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Physical View - Imagine fi le (*.img)

Metadata


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Metadata

Metadata is data about data

Metadata


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Allows a producer to fully describe a dataset sothat users can understand the assumptions and

limitations and evaluate the dataset's

applicability for their intended use.

Metadata

What is Metadata?


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Metadata should contain possible answers for the following

questions:

Who collected the original data and who is responsible for thedataset?

What is the purpose of the dataset?

What will users find from this dataset?

What elements are mandatory and what are optional?

What terminology standard and scales have used in this dataset?

How can users access to the dataset?

What geographic area(s) does this dataset cover?What type of transfer protocol is needed to receive the dataset?

What is Metadata?

What is Metadata?


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Who?

When?

How?What?

Where?

Cost?Purpose?

a a a a

Resume of spatial data

Need for Metadata Standards


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The proper use and effective retrieval of geo-spatial

data to facilitate the organization and managementof geographic data to provide information about an

organization's database to others

Need for Metadata Standards

Metadata standard will promote:

Essential Elements of Metadata for Spatial Information


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1. Identification [IDEN]

2. Data Quality [QUAL]

3. Spatial Data Organization [SDOR]

4. Spatial Reference [SREF]

5. Distribution [DIST]

6. Entity and Attributes Information [ENTI]

7. Metadata Reference [REFE]

sse t a e e ts o etadata o Spat a o at o


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[IDEN] Identification

[TIT] Title: What is the name of the data set?[AUT] Author: Who developed the data set?

[COV] Area Coverage: What geographic area does it cover?

[THE] Themes: What themes of information does it include?

[CUR] Currentness: How current are the data?

[RES] Restriction: Are there restrictions on accessing or using the data?

[QUAL] Data Quality

[ACC] Accuracy: What is the positional and attribute accuracy?

[COM] Completeness: Are the data complete?

[LCO] Logical Consistency: Were the consistency of data verified?

[LIN] Lineage: What data were used to create the data set, and what

processes were applied to those sources?

[SDOR] Spatial Data Organization


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[SDOR] Spatial Data Organization

[VEC ]Vector: Has vector model been used to encode the spatial data?

[RAS] Raster: Has raster model been used to encode the spatial data?

[TNE] Type and Number of Elements: What type and how many spatial

objects are there?

[SREF] Spatial Reference

[PRO] Projection: What map projection method was used to represent the

location of spatial objects?

[LOL] Longitude/Latitude: Are coordinate locations encoded usinglongitude and latitude?

[GRI] Grid System: Is a gird system such as the State Plane Coordinate

System used?

[DAT] Datum: What horizontal and vertical datums are used?[COO] Coordinate System: What parameters should be used to convert the

data to other coordinate system?


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[DIST] Distribution

[DIS] Distributor: From whom can one obtain the data?

[ENTI] Entity and Attributes Information

[FEA] Features: What geographic features are included (roads, houses,

elevation, temperature)?[ATT] Attributes: What characteristics of those features are included?

(lengths, widths, heights)

[AVA] Attribute Values: What parameters are used to represent the

characteristics of features?[FOR] Formats: What formats are available?

[MED] Media: What media are available?

[ONL] Online: Are the data available online?

[PRI] Price: What is the price of the data?


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[REFE] Metadata Reference

[CUR] Currentness of Metadata: When were the metadata compiled?

[RES] Responsible Party: By whom the metadata compiled?[CIT] Citation: Recommended reference to be used for the dataset.

Currently, a number of metadata exist.


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USA: Content Standards for Digital GeospatialMetadata, Federal Geographic Data Committee

(FGDC)

International Organization for Standardization (ISO):ISO CD 15046 - Part 15: Geographic Information -

Metadata

Open GIS consortium (OGC), a private sector

initiative, was formed in 1994 for developing software

specifications to advance geoprocessing inter-

operability across the GIS industry.

OGC has been working very closely with ISO/TC 211 in identifying the

overlap and division of labor in mutual work programs. The formation of

the ISO/TC 211 - OGC coordination group is a result of such efforts.

http: www fgdc gov metadata metadata html

Metadata Example ( Image.Lan File )
http://www.fgdc.gov/metadata/metadata.htmlhttp://www.fgdc.gov/metadata/metadata.html


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Position Field Type

Byte 0 HDWord Char[6]

Byte 6 IPACK (Bits) Short int

Byte 8 NBands Short int

Byte 10 UnUsed Char[6]

Byte 16 IColumn int

Byte 20 IRow int

Byte 24 XStart int

Byte 28 YStart int


Byte 88 MapType Short int

Byte 90 NClass Short int


Byte 106 IAUTYP Short int

Byte 108 ACRE float

Byte 112 XMap float

Byte 116 YMap float

Byte 120 XCell float

Byte 124 YCell float

Data Exchange


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Spatial Data Transfer System (SDTS)

SDTS, a new transfer format developed by the US government,was designed to handle all types of geographic data. SDTS

can be either binary or ASCII but is generally binary.Virtually all geographic concepts can be encoded in SDTS,including coordinate information, complex attributeinformation, and display information. This versatility causes

a corresponding increase in complexity. To simplify things,several standard subsets of SDTS have been adopted. Thefirst of these, the Topological Vector Profile (TVP), is used tostore certain types of vector maps. SDTS can also be used for

raster information. Not much data is available in SDTSformat at this time, nor do many software systems support it.However, it will be the foundation of the US National SpatialData Infrastructure (NSDI). Its importance will increase as

Data Exchange

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