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