Thematic Maps

What is a Thematic map?Thematic maps (statistical maps) are used to emphasize the spatial pattern of one or more geographic attributes (variables).

Examples: Population densityTemperature or pressure variations (weather maps)Family incomeVoting trendsEconomic resources or commodities

The most common type of thematic map is the CHLOROPLETH map. In this map ENUMERATION UNITS (data collection units such as states) are shaded to represent different magnitudes of an attribute.Other varieties of thematic maps are proportional symbol dot maps flow maps (with arrows showing movement) isarithmic maps (variables of equal value are depicted as lines, as on a topographic map)

Flow map: slave migration

What is a general-reference map? They are used to emphasize the LOCATION of spatial phenomena However, they can be conceived as a thematic map in which multiple attributes are displayed simultaneously They can portray spatial patterns like thematic maps:Example: --- the pattern of stream drainage on a USGS topographic map--- the pattern of lake and pond ditsribution in a glaciated area

How are thematic maps used?Provide specific information about particular locationsProvide general information about spatial patternsTo compare patterns on two or more maps

1 & 2. Specific and general information Which map is best for data class recogniton? Which map is best for showing the spatial pattern of voting? How useful are red state vs blue state maps?

3. Pattern comparison

Basic steps for communicating map information:

Step 1:Consider what the real-world distribution of the phenomenon might look like

Step 2: Determine the purpose for making the map

Step 3: Collect data appropriate for the maps purpose

Step 4: Design and construct the map How will the map be used? Will it be used to portray general or specific data? What is the spatial dimension of the data, point, line, areal??? Is data standardization necessary?

Standardized versus non-standardized maps

How many attributes are to be mapped? Is there a temporal component to the map (changes over time)? Technical limitations? What are the characteristics of the target audience? What are time and monetary constraints? Some maps are more expensive to make and reproduce than others.

Step 5: Determine whether users find the map useful and informative

STANDARDIZATION

Non-Standardized mapsChloropleth map Proportional symbol map

Classed and Unclassed maps

Al Fin