GIS Tutorial 1

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GIS Tutorial 1

• Lecture 2
• Map design

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Outline

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

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Choropleth maps

• Lecture 2

4
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 example
Map using color or pattern to show different
values over space (uses a color ramp)
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Choropleth map example

• Percentage of vacant housing units by county

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Classifying data

• Process of placing data into groups (classes or
• bins) 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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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 025, 2550, 5075,75100

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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, 12, 34, 58, 916, 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, 05, 515, 1535, 3575 have interval
  widths of 5, 10, 20, and 40.

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Original map (natural breaks)
U.S. population by state, 2000
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Equal interval scale

• Not good because too many values fall into low
  classes

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Quantile scale

• Shows that an increasing width (geometric) scale
  is needed

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Custom geometric scale

• Experiment with exponential scales with powers of
  2 or 3.

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Normalizing data

• 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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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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Nonnormalized data
California population by county, 2007
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Normalized data
California population density, 2007
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Normalize Data to conform to a standard

• 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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To Create More Meaningful Text in Legends 1.
Left click to highlight the layer in the TOC 2.
Type the desired text 3. When the legend is
added on the layout, the new text will display
TOC
TOC
Layout View
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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

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2
4
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Layout View
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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

Symbol- Flip Symbols
Result
Range- Reverse Sorting
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Other Types of Thematic Maps Graduated Symbols
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Other Types of Thematic Maps Proportional Symbols
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Other Types of Thematic Maps Dot Density
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Other Types of Thematic Maps Unique Values
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colors

• Lecture 2

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Color overview

• 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 wheel

• 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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Light vs. dark colors

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

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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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Dichromatic color scale

• 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 map

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

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Color tips

• Colors have meaning
• Political and cultural
• Cool colors
• Calming
• Appear smaller
• Recede
• Warm colors
• Exciting
• Overpower cool colors

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Color tips

• 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

• 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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Changing colors in ArcMap

• Choose color, more colors

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Learn more about GIS colors

• 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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Vector gis display

• Lecture 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 lines

• For analytical maps, most lines are ground
• features and should be light shades (e.g. gray
• or light brown)

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Displaying lines

• Consider using dashed lines to signify less
• important line features and solid lines for the
• important ones

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Displaying polygons

• Consider using no outline or dark gray for
• boundaries 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 polygons

• Consider using texture for black and white
• copies

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Graphic hierarchy

• 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

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 example
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Gis queries

• Lecture 2

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GIS queries

• Powerful relationship between data table and
  vector-based graphicsunique 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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Simple attribute queries

• Simple query criterion
• ltdata attributegtlt logical operatorgtltvaluegt
• NatureCode 'DRUGS'
• DATE gt '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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Compound attribute queries

• Compound query criteria
• Combine two or more simple queries with the
  logical connectives AND or OR
• "NATURE_COD" 'DRUGS' AND "DATE" gt 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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Layer groups, scale thresholds

• Lecture 2

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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 saved and 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

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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 tips

• Lecture 2

76
Hyperlinks

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

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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