Despite its navigational origin, map is a subcategory of visualization.

Map stands out as a distinctive approach to visualization, as geospatial data is mostly 2-dimensional and sometimes 3-dimensional. To add attributes to maps, point size, line width, shades and color are used instead of length or height. Different attributes can be overlayed for spatial correlation and pattern seeking.

Map Elements

Components of geospatial data:

  • Imagery: aerial, satellite;
  • Raster: measurements embedded in a regular geospatial grid;
  • Vector: geometry or topology; attribute tables;

Visual elements of a map:

  1. Base map (as reference)
  2. Overlay maps (as layers):
    • geometries (as legend);
    • attributes associated with each geometry (as styles);

Map Design

Table: Map Categories by Purpose

Feature Dimension Descriptive Quantitative
points scatterplot (business location) bubble plot (adolescent fertility rate)
lines (roads, mains, sewer, cables) lines w varying width/color (traffic speed)
area categorical map (land-use zoning) choropleth (population density)

Spatial elements:

  • area: polygon, square (many research papers), hexagon (Uber);
  • lines: roads, routes;
  • points: intersection (Geoff Boeing);

Thematic Mapping

Thematic maps are maps designed to show a particular aspect (theme) of a geographic area.

Major thematic mapping techniques:

  1. Dot Distribution Map: dot for presence at a location.
    • Proportional Symbol: symbols of different sizes on regions/locations.
  2. Isopleth Map: isolines of a continuous attribute.
  3. Choropleth Map: shading or color gradient on regions.
    • Dasymetric Map: choropleth map with internal distribution modeled from ancillary information, e.g. using area to calculate density.

Extensions

Advanced extensions of maps may present quantities more accurately, and incorporate the time scale:

  • interactive feature
  • 3D bar chart: population density
  • animation: traffic flow, population growth

Shading (hillshade)

🏷 Category=Geographic Information System