Spatial Data Visualization

Map

• Map provides a powerful way to visualize spatial data
   
• However, sometimes it can be misleading, like many other visualization tools

Cartography

• The art and science of mapmaking
   
• Decisions about:
  -  what data to display
  -  how to display them

Types of Maps in Spatial Epidemiology

• Methods of display:
  -  static map: to show static spatial pattern
  -  animated map: to present spatial pattern over time
   
• Features to display:
  -  maps for points
  -  maps for polygons

Maps for Points

• Point map
  -  delineate the locations of point features
  -  visualization of the spatial pattern of point features
   
• Contour map
  -  made from point features with some attribute values
  -  e.g. air pollution level from stationary monitors

Spatial distribution of sulfate concentrations based on 1980-1981 average values in 144 metropolitan statistical areas

Source: Environmental Health Perspectives Supplements Volume 109, Number S3, June 2001

Maps for Polygons

• Graduated color map (choropleth map)
  -  the most common maps to display polygons
   
• Symbol map
  -  a symbol is located in the centroid of each polygon and attribute values are indicated by the choice of symbol

Maps for Polygons (cont'd)

• Dot densities map
  -  show the amount of an attribute within an area
  -  each dot represents a specified number of features (e.g. each dot represents 1,000 people within an area)
  -  the dots are distributed randomly within each area
  -  the closer together the dots are, the higher the density of features in that area

Maps for Polygons (cont'd)

• Chart map
  -  bar/column charts, stacked bar charts, and pie charts can present large amounts of categorical data in an eye catching fashion

Source: https://www.e-education.psu.edu/natureofgeoinfo/sites/www.e-education.psu.edu.natureofgeoinfo/files/image/hisp_pies.gif

Symbolization

• Location
  -  provide the spatial structure and support of the geographic data
   
• Size
  -  size of points can indicate some attribute values
   
• Shape
  -  different shapes can be used to indicate different types of features
   
• Orientation
   
• Texture and color

Color

Color

• www.colorbrewer.org

Key Elements in A Map

• Title
• Legend
• Neatlines
• North arrow
• Scale
• Source
• Agency

Lab 1: Visualization Using QGIS

git pull