gis tutorial 1 lecture 2 map design. outline choropleth maps colors vector gis display gis...

GIS Tutorial 1

Lecture 2Map design

Outline Choropleth maps Colors Vector GIS display GIS queries Map layers and scale thresholds Hyperlinks and map tips

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CHOROPLETH MAPSLecture 2

Choropleth maps Color-coded polygon maps Use monochromatic scales or saturated

colors Represent numeric values (e.g.

population, number of housing units, percentage of vacancies)

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Choropleth map exampleMap using color or patternto show different values over space (uses a color ramp)

Legend

States

Counties

POP2003

-99 - 162000

162001 - 559264

559265 - 1370157

1370158 - 3581375

3581376 - 9873548

Choropleth map example Percentage of vacant housing units by

county

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Classifying dataProcess of placing data into groups (classes orbins) that have a similar characteristic or

value

Break points Breaks the total attribute

range up into these intervals Keep the number of intervals

as small as possible (5-7) Use a mathematical progression

or formula instead of picking arbitrary values

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Break points

How to classify ranges in ArcMap

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Classifications

Natural breaks (Jenks) Picks breaks that best group similar values

together naturally and maximizes the differences between classes

Generally, there are relatively large jumps in value between classes and classes are uneven

Based on a subjective decision and is the best choice for combining similar values

Class ranges specific to the individual dataset, thus it is difficult to compare a map with another map

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Classifications Quantiles

Places the same number of data values in each class

Will never have empty classes or classes with too few or too many values

Attractive in that this method produces distinct map patterns

Analysts use because they provide information about the shape of the distribution.

Example: 0–25%, 25%–50%, 50%–75%,75%–100%

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Classifications

Equal intervals Divides a set of attribute values into

groups that contain an equal range of values

Best communicates with continuous set of data

Easy to accomplish and read Not good for clustered data

Produces map with many features in one or two classes and some classes with no features

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Classifications

Use mathematical formulas when possible.

Exponential scales

Popular method of increasing intervals Use break values that are powers such as 2n or 3n

Generally start out with zero as an additional class if that value appears in your data

Example: 0, 1–2, 3–4, 5–8, 9–16, and so forth

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Classifications

Use mathematical formulas when possible

Increasing interval widths

Long-tailed distributions Data distributions deviate from a bell-shaped

curve and most often are skewed to the right with the right tail elongated

Example: Keep doubling the interval of each category, 0–5, 5–15, 15–35, 35–75 have interval widths of 5, 10, 20, and 40.

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U.S. population by state, 2000

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Original map (natural breaks)

Not good because too many values fall into low classes

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Equal interval scale

Shows that an increasing width (geometric) scale is needed

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Quantile scale

Custom geometric scale Experiment with exponential scales with

powers of 2 or 3.

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Divides one numeric attribute by another in order to

minimize differences in values based on the size of

areas or number of features in each area

Examples: Dividing the number of vacant housing units by

the total number of housing units yields the percentage of vacant units

Dividing the population by area of the feature yields a population density

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Normalizing data

Nonnormalized data

Number of vacant housing units by state,

2000

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Normalized data

Percentage vacant housing units by state,

2000

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California population by county, 2007

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Nonnormalized data

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California population density, 2007

Normalized data

Normalize Data to conform to a standard

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•Right-click the layer you want to draw showing a quantitative value in the table of contents and click Properties. •Click the Symbology tab. •Click Quantities and click graduated colors. •Click the Value drop-down arrow and click the field that contains the quantitative value you want to map. •Click the Normalization drop-down arrow and click a field to normalize the data. •ArcMap divides this field into the Value to create a ratio.

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TOC TOCLayout View

To Create More Meaningful Text in Legends

1. Left click to highlight the layer in the TOC2. Type the desired text3. When the legend is added on the layout, the new text will display

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OR- To Create More Meaningful Text in Legends

• 1 In Layout View, right click the legend box• 2 Select Convert To Graphics • 3 Right click the Graphics text box legend, select Ungroup• 4 Double left click text, then type desired text

Layout View

1

2

3 4

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To sort value ranges in descending order: •Right-click the layer you want to draw showing a quantitative value in the table of contents and click Properties. •Click the Symbology tab. •Click Quantities and click graduated colors. •Click the Value drop-down arrow and click the field •that contains the quantitative value you want to map. •Click the Range tab and click Reverse Sorting. •ArcMap places the ranges in descending order.•Select OK

To reverse the symbol color:•Select the symbol tab•Select Flip Symbols•Select OK

Range- Reverse Sorting

Symbol- Flip Symbols

Result

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Other Types of Thematic Maps: Graduated Symbols

Percent

5.9 - 13.3

14.2 - 19.3

20.0 - 25.8

28.1 - 37.3

Percent Poverty By County, 1990

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Other Types of Thematic Maps: Proportional Symbols

20

Percent

Percent Poverty By County, 1990

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1 Dot = 1 Percent

Percent Poverty By County, 1990

Other Types of Thematic Maps: Dot Density

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Other Types of Thematic Maps: Unique Values

COLORSLecture 2

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Hue is the basic color

Value is the amount of white or black in the color

Saturation refers to a color scale that ranges from a pure hue to gray or black

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Color overview

33

Device that provides guidance in choosing colors

Use opposite colors to differentiate graphic features

Three or four colors equally spaced around the wheel are good choices for differentiating graphic features

Use adjacent colors for harmony, such as blue, blue green, and green or red, red orange, and orange

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Color wheel

Light colors associated with low values Dark colors associated with high values Human eye is drawn to dark colors

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Light vs. dark colors

Contrast

The greater the difference in value between an

object and its background, the greater the

contrast

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Monochromatic color scale Series of colors of the same hue with

color value varied from low to high Common for choropleth maps The darker the color in a

monochromatic scale, the more important the graphic feature

Use more light shades of a hue than dark shades in monochromatic scales The human eye can better differentiate

among light shades than dark shades

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Monochromatic map

Values too similar

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Monochromatic map

A better map, more contrast

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An exception to the typical monochromatic scale used in most choropleth maps

Two monochromatic scales joined together with a low color value in the center, with color value increasing toward both ends

Uses a natural middle point of a scale, such as 0 for some quantities (profits and losses, increases and decreases)

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Dichromatic color scale

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Symmetric break points centered on 0 make it easy to interpret the map

Dichromatic map

Color tips Colors have meaning

Political and cultural

Cool colors Calming Appear smaller Recede

Warm colors Exciting Overpower cool colors

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Do not use all of the colors of the color spectrum, as seen from a prism or in a rainbow, for color coding

If you have relatively few points in a point layer, or if a user will normally be zoomed in to view parts of your map, use size instead of color value to symbolize a numeric attribute

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Color tips

43

If you have many polygons to symbolize, it is better to

use polygon centroid points with color rather than

polygon choropleth maps.

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Color tips

Changing colors in ArcMap

Choose color, more colors…

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Website http://colorbrewer2.org/

Books Brewer, Cynthia A. 2008. Designed Maps: A

Sourcebook for GIS Users. Redlands: ESRI Press

Brewer, Cynthia A. 2005. Designing Better Maps: A Guide for GIS Users. Redlands: ESRI Press

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Learn more about GIS colors

VECTOR GIS DISPLAYLecture 2

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Points, lines, polygons Point

x,y coordinates Line

starting and ending point and may have additional shape vertices (points)

Polygon three or more lines joined to form a closed

area

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Feature attribute tables Store characteristics for vector features Layers can be displayed using

attributes

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Displaying points Single symbols All CAD calls

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Displaying points Same features, different points Based on attributes

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Displaying points Industry specific (e.g. crime analysis) Good for large scale (zoomed in) maps

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Displaying points Industry specific (e.g. schools)

Not good for multiple features at smaller scales

Simple points better for analysis

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Displaying points Quantities

Use exaggerated sizes

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Displaying linesFor analytical maps, most lines are

groundfeatures and should be light shades (e.g.

grayor light brown)

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Displaying linesConsider using dashed lines to signify

lessimportant line features and solid lines for

theimportant ones

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Displaying polygonsConsider using no outline or dark gray forboundaries of most polygons

Dark gray makes the polygons prominent enough, but not so much that they compete for attention with more important graphic features

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Displaying polygonsConsider using texture for black and

whitecopies

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Assign bright colors (red, orange, yellow, green, blue) to important graphic elements

Features are known as figure

All features in figure

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Graphic hierarchy

Assign drab colors to the graphic elements that provide orientation or context, especially shades of gray

Features known as ground

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Circles in figure, squares and lines in ground

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Graphic hierarchy

Place a strong boundary, such as a heavy black line, around polygons that are important to increase figure

Use a coarse, heavy cross-hatch or pattern to make some polygons important, placing them in figure

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Graphic hierarchy

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Graphic hierarchy example

GIS QUERIESLecture 2

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Powerful relationship between data table and vector-based graphics—unique to GIS

Records from a feature attribute table are selected by using query criteria

Query will automatically highlight the corresponding graphic features

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GIS queries

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Simple query criterion <data attribute>< logical operator><value> NatureCode ='DRUGS' DATE >= '20040701'

% wild card % symbol stands for zero, one, or more

characters of any kind NAME like ' BUR%' Selects any crime with names starting with

the letters BUR, including burglaries (BUR), business burglaries(BURBUS), and residential burglaries (BURRES)

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Simple attribute queries

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Simple attribute queries

66

Compound query criteria Combine two or more simple queries with

the logical connectives AND or OR "NATURE_COD" = 'DRUGS' AND "DATE" >

20040801 Selects records that satisfy both criteria

simultaneously Result are drug crimes that were committed

after August 1, 2004

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Compound attribute queries

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Compound attribute queries

LAYER GROUPS, SCALE THRESHOLDS

Lecture 2

Layer groups Organizes layers Groups and names logically

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Map Layer file (.lyr)

Display certain characteristics of a dataset

Show street subset that is classified by small, medium, or large

Dataset properties such as color & line width are savedand applied to similar datasets.

To create layer file

-right click layer-Select Save as layer file-type layer filename

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Group Layer (.lyr)

To create a Group Layer:

-Right click the data frame text and Select New Group Layer

-Select the New Group layer & Add Data (i.e.rail & interstate)

-Right click the New Group layer text and select Save as Layer File

-In the save layer pop up window, type the name of the new layer file

i.e. Transportation Group.lyr

Minimum scale threshold When zoomed out beyond this scale,

features will not be visible Tracts not visible when zoomed to the USA

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Minimum scale threshold

Tracts displayed when zoomed in

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Maximum scale threshold When zoomed in, features will not be

visible State population will disappear when

zoomed in to a state

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HYPERLINKS AND MAP TIPSLecture 2

Links images, documents, Web pages, etc. to features on a map

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Hyperlinks

Map tips Provide an additional way to find

information about map features Pop up as you hover the mouse pointer

over a feature

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Summary Choropleth maps Colors Vector GIS display GIS queries Map layers and scale thresholds Hyperlinks and Map tips

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