Simulic
English

Thematic maps – choropleth, dot, isoline, class breaks and scale

GeographyMaps & MappingAges 15–16

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One census of a fictional continent (population density, unemployment rate and daily commuters) can be drawn as a choropleth, proportional symbol, dot, isoline or flow-line map. Change the class breaks (equal interval, quantile, natural breaks), the number of classes, the unit of aggregation and the scale of analysis (continent, country, state, county) and watch the pattern and the conclusion change; a ratio scale, line scale, statement scale and two points A and B let you measure distances.

Lesson: Thematic maps: choropleth, proportional symbol, dot density, isoline and flow-line maps; data classification; unit of aggregation and scale of analysis; map scale and measuring distance

What it shows

Thematic maps show one theme, such as population density or unemployment, and every map is a set of choices. This simulation maps one synthetic census of a fictional continent in five ways: choropleth, proportional symbol, dot density, isoline and flow-line. The same numbers produce different patterns when the class breaks, the number of classes or the areal units change (the modifiable areal unit problem), and when the scale of analysis moves from continent to country, state or county. Every map shows a ratio scale, a statement scale and a line scale for measuring distances.

How to use

Choose the Scale, the Data and the Map. For choropleth and isoline maps, change Class breaks and Classes and read the histogram and the top-class line. Change the Unit, and tap the map to pick the place you study. Tick Measure A–B and drag A and B to measure a distance. Press Add to table to compare maps.

Parameters you can change

  • Scale of analysis Continent, Country, State, County
  • Data shown Population density, Unemployment rate
  • Map type Choropleth, Proportional symbols, Dot density, Isolines, Flow lines
  • Unit of aggregation Country, State, County, County (other boundaries), Census tract
  • Class breaks Equal interval, Quantile (equal count), Natural breaks (Jenks)
  • Number of classes 3–7
  • Measure distance A–B

Questions to explore

  1. Why does equal interval put most counties into the lowest density class?
  2. Does a county in the top class for the whole country stay in the top class within its own state?
  3. Why do the dot map and the flow-line map lose almost all detail when the unit is a whole country?

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