Data Storage and Processing

GIS Topics and Applications

GIS Models Over Time

• Simple Representation– CAD model

• Data Analysis– Raster model

• Data Collection– Vector model

• Relational and Rules– Object model

Coding Vector GIS

PolygonI

PolygonII

PolygonIII

PolygonV

PolygonIV

node

A

node

Bnode

C

node

E node

F

node

G

node

D

Reality Vector Mode Model of Reality

You’ve seen this before.

Let’s break it down.

PolygonI

PolygonII

PolygonIII

PolygonV

PolygonIV

node

A

node

Bnode

C

node

E node

F

node

G

node

D

PolygonI

PolygonII

PolygonIII

node

A

node

Bnode

C

node

E node

Fnode

D

A topologic vector model records the points and linesshared between polygons as unique items, thus every oneof the points and lines are recorded in the data only once.

PolygonII

node

A

node

Bnode

C

node

E

node

D

Polygon 2 is on the right sideof the line ABCED.

PolygonI

PolygonII

PolygonIII

PolygonV

PolygonIV

node

Anode

E node

Fnode

D

Polygon 2 knows it’s adjacent to Polygons 1, 3, & 4.It shares a line segment with each.

Polygon 2 knows it touches Polygon 5.It shares node E with Polygon 5.

PolygonI

PolygonII

PolygonIII

PolygonV

PolygonIV

node

A

node

Bnode

C

node

E node

F

node

G

node

D

Strict Topology

• Features are composed from a common set of points and lines.

• Altering the vertices of one polygon affects polygons that share those vertices.

• Harder to introduce gaps or slivers.

Objects

• GIS Features as Objects is a recent method of representing aspects of the real-world in GIS

• Example of the shift from specialty data to DBMS that are spatially-aware

• Non-planar, temporally shifting, topologically linked, rule-based actions

• Still important to check for topology to ensure as a quality control step

Vector Geometry as Objects

• Parcels– Planar geometries with attribute information

• Parcels as objects in a Cadastral “carpet”– Objects with topology rules (“don’t overlap, unless”)– Members of “regional” features (zoning, municipality)– Composed of surveyed parts (COGO, benchmarks)– Keys that link to attribute tables (owner(s), assessments,

plans, etc)

Cadastre Example

benchmark survey (COGO) parcels zones

Attributes as Objects• Not only can multiple sets of geospatial features interact

with rules, the attributes can be linked with one another, with their own set of rules and actions

• Ownership record linked to GIS parcel– Search on multiple owners, records– Removal of parcel warns about “orphan” owner

• Functions that can be performed by GIS analyst can be embedded in the actual database

Manipulating Vector Mode Databases

Common Operations

• Selection by Attributes or Location• Dissolve• Append• Clip• Intersect• Union

Select by Attributes

• Create WHERE clauses that match a subset of the features in a vector dataset.

• WHERE clauses are a part of Structured Query Language (SQL)

• Analogous to "Find" in some other software.• Match all records where…– "COUNTY" = 'Gloucester'– NOT "TYPE" = 'Wetlands'– "POP2000" > 100000

Select by Location

• Proximity or overlay based on features in one layer and features in another layer or the same layer.

• Several methods to compare proximity & overlay– Distance from– Touching (on edge)– Contains or Within– Partial Overlaps– Exact Matches

Dissolve

Dissolve FeaturesInput Output

Append

Layers to Append

Input Layer 1 Input Layer 2

Appended Layers

Overlapping Polygons/Polylines are preserved!

Clip

Output Layer

Clipped Features

Input Layer & Clipping Layer

Input Layer

Clip Polygon

Intersect

Intersection

• Where are the Road segments that are in flood prone areas.

• Select flood prone from Input Layer 1

• Intersect roads and flood prone [Layer 2].

Stream

No Flood

FloodProne

Intersect Features

Input Layer 1

Roads

Input Layer 2

Panel 1

Stream

No Flood

FloodProne

Intersect Features

Input Layer 1

Input Layer 2

Roads

Question: where are the road segments that pass through flood prone areas?

Panel 1

Stream

No Flood

FloodProne

Intersect Features

Roads

Input Layer 1

Input Layer 2

Select flood prone areas and then intersect Input Layer 1 with Layer 2 Roads.

Panel 2

Study Area

FloodProne

Intersect Features

Output Layer

Roads that pass through flood prone areas. Attributes of both layers maintained in table.Length of roads in flood areas becomes attribute

Roads

Panel 3

Intersection

• Where are the places that are residential and flood prone?

• Select flood prone from Input Layer 1• Select residential from Input Layer 2• Intersect

Stream

No Flood

FloodProne

Intersect Features

Input Layer 1

Panel 1

Intersect Features

Input Layer 2

Residential

CommercialIndustry

Open space Panel 2

Stream

No Flood

FloodProne

Intersect Features

Input Layer 1

Input Layer 2

Residential

CommercialIndustry

Open space Panel 3

Extent

Intersect Features

Output Layer

Residential &Flood Prone

Panel 4

Panel 1

Panel 2

Panel 3Panel 4

Union

Agricultural Land Use

Corn

Green Beans

Tomatoes

Wheat

Panel 1

Soil Quality

Poor

Fair

Good

Excellent

Panel 2

Agricultural Land Use

Corn

Green Beans

Tomatoes

Wheat

Soil Quality

Poor

Fair

Good

Excellent

Corn &Poor Green Beans & Poor

Green Beans & Fair

Tomatoes & Fair

Tomatoes & Good

Wheat & Good

Wheat & Excellent

Corn & Excellent

Panel 3

Let’s See How It Works

Dissolve

Dissolve Operation

1. Right Click

2. Click to select.

1. Click to open menu

2. Click to open Add Field dialog

Add Field for Dissolve

Type a name and click OK

Name and Type of Field for Dissolve

Table with Code Field

Resulting field

DoubleClick

Click

Click

Do the Dissolve

4

2

3

1

Dissolve Dialog

Dissolve

Click

Click

DoubleClick

Append Operation

4

2

3

1

Append Dialog

AppendTwo layers before append One layer after append

Click

Click

DoubleClick

Clip Operation

2

3

1

Clip Dialog

ClippingRoads before clipping Roads after Clipping

Intersection

Intersection Procedure

• Where are the areas that are residential in land use and flood prone?– Select flood prone areas from flood prone layer– Select residential areas from land use layer– Do intersection

Intersect

Residential

Select by Attributes Dialog

Selecting flood prone and water areas

Select by Attributes Dialog

Selecting residential areas

Click

Click

DoubleClick

Intersection Operation

4

2

3

1

56

Intersection Dialog

Remember, if you did a selection, then get input features from drop down or drag into dialog from TOC

Intersection Result

Intersection

Result

Union

Click

Click

DoubleClick

Union Operation

4

2

3

5

1

Union Dialog

This map depicts land use patterns for a portion of Washington Township prior to performing the union operation in which land use and flood prone layers were overlain.

This map depicts land use patterns for a portion of Washington Township after performing the union operation in which land use and flood prone layers were overlain. Notice that some of the land use polygons have been cut creating new polygons. This occurs in areas in which a polygon from the flood prone layer intersects a land use polygon. The attributes of the new layer enable the analyst to map the coincidence of each land use category with each flood proneness category.