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

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Introduction to GIS

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

Vector

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Point layerX,Y coordinates

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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

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

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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

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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.

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Raster and Vector representations of the same terrain

Raster: great for surfaces Vector: limited with surfaces

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Raster and Vector representations of the same

land use:

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Vector vs. Raster: bounding

Raster: bad with bounding Vector: boundary precision

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Vector vs. Raster: Sample pointsCancer rates across space

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Vector / Raster RepresentationPoints

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Vector / Raster RepresentationLines

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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

Mapping Attribute Data

Quantity approach: applies to numeric >> ordinal

Category approach: text values; order is irrelevant

Introduction to GIS

Mapping Attribute Data

Quantity approach, example: population

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Mapping Attribute Data

Category approach, example: vegetation type

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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

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Mapping Categories

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

map had over 110 categories that were condensed to 12

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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

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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

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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

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Graduated ColorThe map shows high value housing with dark

colors and low value housing with light colors

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Graduated ColorSame map, but this time with 3 classes

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Graduated Color…and with 15 classes

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Graduated Color Classification

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

largesmall

Classification method (default= Jenks)

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Graduated Color

• Classification Method: Equal Interval

• What kind of data does this work for?

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Graduated ColorHere’s what the same

distribution looks like with only 5 equal intervals.

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Graduated Color

• Data representing # of vacant structures

• Potential problem(s) with this method of classification

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Graduated Color

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

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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

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Graduated Color

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

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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

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Graduated Color

Map of vacant properties using the Quantile classification method

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Graduated ColorGraduated color can also be applied to points.

Here are houses display by sales price

Natural breaks Equal interval

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Graduated SymbolIn this case housing price is expressed by symbol size

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Graduated SymbolThe same thing can

also be done with lines—for instance, traffic volumes

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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

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Symbol Styles

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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.

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Includes many classes of industry standard symbols

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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

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

displayed as charts on the map

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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.

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numerator

denominator

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Layer Files

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• 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

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Layer Files

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

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Layer Files

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• Create a layer file in ArcCatalog

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Layer Files

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• Create a layer file in ArcMap

Introduction to GIS

Layer Files

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• Import a layer file’s symbology in properties

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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

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Map Compilation

Map?X

What’s missing?

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Title

Legend

Neatline

North arrow

Scale bar

Notes

Data frame

Map Compilation

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Map Compilation• Geographic features

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

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

ArcMap

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

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Frame 1

Frame 2

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Data Frames: Context

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Data Frames: Inset maps

Introduction to GIS

Layouts: Data frame• Access and edit data frame properties

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Map Layout: Map Legend

Introduction to GIS

Map Layout: Map Legend

Introduction to GIS

• Legends editing: Items

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Insert Legend Title

Map Layout: Map Legend

Introduction to GIS

Map Layout: Map LegendEditing legend item type

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Map Layout: Map Legend

Introduction to GIS

• Legends editing: Size and position

Size&Position

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Map Layout: North Arrows

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Map Layout: Scale Bar

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MXD Files

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• Project files– Save your layout

– All other preferences

– Data is not included

– With an extension .mxd

• File >>> Save (As)