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Class 8

Introduction to Mapping

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AGENDA

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Today’s Class …

  • Types of Mapping
  • Why are Maps Important?

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During Class …

  • Transforming spatial data

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Next Class …

  • Mapping In Class Activity

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Why create maps?

  • Allows for visual interpretation of geographic patterns of phenomena
    • Are locations clustered?
  • Variation of a type or value
    • Are values clustered?

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Map Types

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    • communicate spatial association between various phenomena
    • e.g., roads, settlements, administrative boundaries, water bodies, etc.

Reference

    • communicate the distribution of a single property or relationships among several

Thematic

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Examples – Reference Map

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Examples – Thematic Maps

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Map Types – Point Map

  • Variable of interest is represented as set of point features
  • e.g., disease events, facilities, wells
  • Symbology is held constant (all points have the same shape, color, and size)
    • Visual interpretation of the density of events (per area) via the locations of points on the map
  • Data integration
    • Compare density to other features

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Map Types – Categorical Point Map

  • Variable of interest is represented as set of point features, with categorical differentiation
    • Not quantitative!!
  • Symbology is held constant except for shape or color (not size!!)

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Map Types - Proportional Symbol Map

  • Variable of interest is represented as set of point features, with interval/ratio
  • information
    • e.g., number of disease cases
    • Can also work with line data
  • Size of symbol is scaled proportionally to the value of the attribute
  • Data integration
    • Compare location and number of cases to other features

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Map Types – Categorical Map

  • Variable of interest is categorical information for areal data
    • Not quantitative
  • Vary the color of the symbology to distinguish categories

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Map Types – Choropleth Maps

  • Variable of interest represented by ratios/rates/proportions located within areal features (polygons)
    • We generally do not use counts
    • Areas are shaded with different colors, patterns, or intensities
      • Shows geographic variation
      • Requires classifying or binning the data values

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Choropleth Map Cntd

  • Variable of interest represented by ratios/rates/proportions located within areal features (polygons)
    • We generally do not use counts
    • Areas are shaded with different colors, patterns, or intensities
      • Shows geographic variation
      • Requires classifying or binning the data values

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Map Types – Choropleth Maps

  • Data Classification
  • Our eyes are not good at discerning more than 6- 8 different shades of color in one map
    • Values (attribute that is being mapped) are classified or binned into classes
    • Each class is assigned a specific color along a color ramp
    • Value or Saturation sequence

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Examples - Choropleth Maps

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Map Types – Choropleth Maps

  • Data Classification methods
  • Uses the distribution of values (histogram)
    • Equal Interval
      • Divides range of all data into categories of equal range Quantiles
    • Quantiles
      • Divides range of all data into n categories such that the same number of features are in each category
  • Natural Breaks
    • Finds natural groupings in the data
    • Result is usually somewhere between equal interval and quantiles

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Why this Matters?

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Map Types – Choropleth Maps

  • Classification Guidelines
    • Equal interval is not appropriate for a highly skewed distribution, but value ranges are easier to interpret
    • Quantiles can highlight differences among the features, but can result in large differences in the value ranges
    • Natural breaks (ArcMap default) can balance these concerns and find gaps in the distribution, but value ranges are uneven

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Mapping Design - Color

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Source: https://www.esri.com/arcgis-blog/products/js-api-arcgis/mapping/better-colors-for-better-mapping/

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Color- Number of Colors

  • The eye can only process a small number of colors at any one time.

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Color- Color Selection

  • Should be based on the variable you are attempting to map
  • Should consider color interpretations
  • Should create a harmonious color field
  • Should consider accessibility

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Colors- Culture

https://robslink.com/SAS/democd93/colors_in_cultures.htm

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Map Design- Legibility

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Map Design- Visual Hierarchy

  • What is the most important thing on your map- what are you trying to “say” with your map?

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https://open.maricopa.edu/gist/chapter/4-3-map-examples/

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