introduction to gis lecture 2: part 1. understanding spatial data structures part 2. legend editing...

Introduction to GIS

Lecture 2:Part 1. Understanding Spatial Data

Structures

Part 2. Legend editing & choropleth mapping

Part 3. Map layouts

Introduction to GIS

Part 2. Spatial Data Structures

By Austin Troy & Brian Voigt

Introduction to GIS

Spatial Data Model

• Features– cartographic object

• Entities– spatial location– non-spatial properties

Introduction to GIS

Introduction to GIS

• Points (no dimensions)• Lines, or “arcs” (1 dimension) or• Areas, or “polygons” (2 or 3 dimensions)

Vector

Introduction to GIS

Point layerX,Y coordinates

Introduction to GIS

0 5

1

1 2 3 4

2

3

4

5 Point ID Location

1 4,3

2 2,2

3 1,4

4 4,1

1

2

3

4

Examples: Stream gauge / wave buoy, stoplight, survey location / respondent, residence / business, etc.

Introduction to GIS

Line (Arc) layer• Points define lines (arcs)

Introduction to GIS

Image source: ESRI Arc Info electronic help

Line segment

Vertex

Node

• Feature is the ARC, not the line segments• Arcs meet at the nodes

Arc

Introduction to GIS

Line (Arc) layer• Each point has a unique location

Introduction to GIS

Introduction to GIS

Polygon layer• In a polygon layer, lines (arcs) define areas

Introduction to GIS

Lines (Arcs)

Points

• Boundaries: line segments

• Area of homogenous phenomena

• Closed region

Introduction to GIS

Raster

• Grids, or pixels• Cell size is constant• Area of each cell defines the resolution • Raster files store only one attribute, in the

form of a “z” value, or grid code.

Introduction to GIS

Raster and Vector representations of the same terrain

Raster: great for surfaces Vector: limited with surfaces

Introduction to GIS

Raster and Vector representations of the same

land use:

Introduction to GIS

Vector vs. Raster: bounding

Raster: bad with bounding Vector: boundary precision

Introduction to GIS

Vector vs. Raster: Sample pointsCancer rates across space

Introduction to GIS

Vector / Raster RepresentationPoints

Introduction to GIS

Vector / Raster RepresentationLines

Introduction to GIS

Vector / Raster RepresentationPolygons

Introduction to GIS

WHEN TO USE RASTER OR VECTOR???

Introduction to GIS

•Raster and Vector

• Analytic advantage and disadvantages• Technical advantages and disadvantages• Specific Usages• Tossups

Introduction to GIS

Part 2. Legend editing, choropleth mapping

By Austin Troy & Brian Voigt

Introduction to GIS

Mapping Attribute Data

Two basic approaches for visually displaying attribute data:

1. Quantities approach

2. Category approach

Introduction to GIS


Quantity approach: applies to numeric >> ordinal

Category approach: text values; order is irrelevant

Introduction to GIS


Quantity approach, example: population

Introduction to GIS


Category approach, example: vegetation type

Introduction to GIS

Mapping Categories

Examples: vegetation types, land use, soil types, geology types, forest types, party voting maps, land management agency, recategorizations of numeric data (“bad, good, best” or “low, medium, high’). Can you think of any others?

Introduction to GIS

Mapping Categories

• Access layer properties: 1. right-click layer in the TOC

2. double-click layer in TOC

• Symbology tab >>> Categories >>> Unique values

• Set Value Field to desired attribute

• Click the Add All Values button

Introduction to GIS

Mapping Categories

Introduction to GIS

Mapping CategoriesOften categories must be aggregated and redefined: this land use

map had over 110 categories that were condensed to 12

Introduction to GIS

Grouping Categories

In this case 1262, 1263, 1264, 1265, etc. refers to different subcategories of commercial land use

Can then save symbology as .lyr or in .mxd

Introduction to GIS

Quantity Mapping

Also known as “choropleth mapping”• For points, lines and polygons: graduated color,

or color ramping• For lines and points can also do graduated

symbol

Introduction to GIS

Graduated Color

• Layer Properties >>> Symbology >>> Quantities >>> Graduated colors

• Set the Value field to desired attribute• In this case we choose median house

value• It automatically assigns

five classes for the data

Introduction to GIS

Graduated ColorThe map shows high value housing with dark

colors and low value housing with light colors

Introduction to GIS

Graduated ColorSame map, but this time with 3 classes

Introduction to GIS

Graduated Color…and with 15 classes

Introduction to GIS

Graduated Color Classification

interfaceThese are the class breaks (based on the distribution of the data)

largesmall

Classification method (default= Jenks)

Introduction to GIS

Graduated Color

• Classification Method: Equal Interval

• What kind of data does this work for?

Introduction to GIS

Graduated ColorHere’s what the same

distribution looks like with only 5 equal intervals.

Introduction to GIS

Graduated Color

• Data representing # of vacant structures

• Potential problem(s) with this method of classification

Introduction to GIS

Graduated Color

This map of vacant properties tells us almost nothing, because almost all the records fall into the first class

Introduction to GIS

Graduated Color• Natural Breaks: Notice

how there are now more classes on the left side, where most of the data are.

• Minimize each class’s average deviation from the class mean, while maximizing each class’s deviation from the means of the other groups

• Reduce the within class variance and maximize the between class variance

Introduction to GIS

Graduated Color

This map of vacant properties, made with Natural Breaks, is more intelligible

Introduction to GIS

Graduated Color

Quantile method: sets the class boundaries so as to maximize the perceived variation in the map; equal number of data points in each class

Introduction to GIS

Graduated Color

Map of vacant properties using the Quantile classification method

Introduction to GIS

Graduated ColorGraduated color can also be applied to points.

Here are houses display by sales price

Natural breaks Equal interval

Introduction to GIS

Graduated SymbolIn this case housing price is expressed by symbol size

Introduction to GIS

Graduated SymbolThe same thing can

also be done with lines—for instance, traffic volumes

Introduction to GIS

Symbol StylesWe can also choose to “match to symbols in a palette” and then

apply the “transportation.style” palette to the FCC, or roadcategory, attribute inour roads layer

Introduction to GIS

Results in this map

Must click here to match

Choose your style palette here

Introduction to GIS

Symbol Styles

Introduction to GIS

Symbol StylesOne could also manually create symbol styles for each street type.

Clicking on each symbol in either the TOC or properties windows brings up a manual symbol selector. You can assign a separate one to each category.

Introduction to GIS

Includes many classes of industry standard symbols

Introduction to GIS

Symbol StylesThere are also a huge variety of industry-specific point symbols

that can be either assigned through matching symbols to a predefined style or manually assigning those symbols

Introduction to GIS

Introduction to GIS

Displaying ChartsAttributes for point, line or polygon features can also be

displayed as charts on the map

Introduction to GIS

Introduction to GIS

NormalizationShow an attribute normalized by another attribute or

expressed as a percentage of total. Here we have number of vacancies per tract as a percentage of total households.

Introduction to GIS

numerator

denominator

Introduction to GIS

Layer Files

Introduction to GIS

• Save symbology and setting

• Primarily for saving legend setting

• Opening a layer file will open the data layer with all the preferences saved

• With an extension .lyr

Introduction to GIS

Layer Files

Introduction to GIS

• Use layer files when you have lots of non-numeric categories

Introduction to GIS

Layer Files

Introduction to GIS

• Create a layer file in ArcCatalog

Introduction to GIS

Layer Files

Introduction to GIS

• Create a layer file in ArcMap

Introduction to GIS

Layer Files

Introduction to GIS

• Import a layer file’s symbology in properties

Introduction to GIS

Part 3. Map Layouts

By Brian Voigt and Austin Troy

Introduction to GIS

Map Layout• You can create a map for layout in Arc GIS

by selecting View >>> Layout view.• Layouts are designed to be cartographically

acceptable, which means they must have the key elements of a printed map, such as scale bars, north arrows, legends and titles

• These can be added from the Insert menu

Introduction to GISIntroduction to GIS

Map Compilation

Map?X

What’s missing?


Title

Legend

Neatline

North arrow

Scale bar

Notes

Data frame

Map Compilation


Map Compilation• Geographic features

• Other map elements– Legend– Title– North arrow– Scale bar– Author– Neatline– Source of data– Other objects…

Introduction to GIS

Map Layout: Data frame• Create a new view or “Data Frame” in

ArcMap

Introduction to GIS

Introduction to GIS

ArcMap: Data Frame• More than one frame can be shown in layout view

Introduction to GIS

Frame 1

Frame 2

Introduction to GIS

Data Frames: Context

Introduction to GIS

Data Frames: Inset maps

Introduction to GIS

Layouts: Data frame• Access and edit data frame properties

Introduction to GIS

Introduction to GIS

Map Layout: Map Legend

Introduction to GIS


Introduction to GIS

• Legends editing: Items

Introduction to GIS

Insert Legend Title


Introduction to GIS

Map Layout: Map LegendEditing legend item type

Introduction to GIS


Introduction to GIS

• Legends editing: Size and position

Size&Position

Introduction to GIS

Map Layout: North Arrows

Introduction to GIS

Map Layout: Scale Bar

Introduction to GIS

MXD Files

Introduction to GIS

• Project files– Save your layout

– All other preferences

– Data is not included

– With an extension .mxd

• File >>> Save (As)

introduction to gis lecture 2: part 1. understanding spatial data structures part 2. legend editing...

Documents