Thematic Map?
- What is Thematic Map?
- Types of Thematic Maps
Making a Map
- Planning
- Data Mapped: Measurement scales
- Symbology
- Symbols
- Colors and Color Schemes
- Data Normalization
- Data Classification
An Example
2023-01-27
Thematic Map?
Making a Map
An Example
Source: Redrawn from Thematic Map Design, by Borden Dent.
Thematic map: a map that shows the spatial distribution of one or more geographic phenomena.
A thematic map is made up of two main components: the geographic basemap, and the overlay of the thematic data. In thematic maps, your main subject (the information you try to convey) is distinctly visible against the base map, rising to the top of your visual hierarchy.
Based on how the data is mapped, the applied visual variable, and symbol dimensionality, there are different types of thematic maps:
Accordingly, each thematic map suggests a different way of thinking about the same mapped phenomenon, and thus may lead to different insights and conclusions about the represented topic (MacEachren & DiBiase, 1991; Kraak et al., 2020).
Choropleth maps are perhaps the most frequently used thematic maps for portraying statistical data!
An isoline map (contour map) is a thematic map that represents data with lines derived through interpolation that connect points of equal attribute value on a map. The lines are called isolines or isarithms.
A dasymetric map is a thematic map that uses ancillary data to determine new more meaningful borders of enumeration units, improving the representation of the spatial distribution of the mapped phenomenon.
Two kinds of ancillary data:
It is common to plot more than one variable on a map by using two thematic map types, and these are referred to as bivariate maps.
[source: Maantay and Ziegler, 2006]
Choropleth map
Strengths:
Limitations:
Proportional / graduated symbol map
Strengths:
Limitations: not very reader/user friendly
Isoline/isarithmic map
Strengths:
Limitations:
Dot density map
Strengths:
Limitations:
Dasymetric map
Strengths:
Limitations:
Before you make any map, ask yourself these crucial questions:
Each scale is represented once in the list below.
Common Parameters (visual variables) of Symbols
Color Scheme:
Data Normalization and classification should be strongly considered in all types of aggregated mapping!!!
Classification is an important and critical process in thematic storytelling
Changing a classification scheme can modify the message of the map entirely
Be objective and honest ( May the force be with map-maker)
Some practical guidance:
You need to do data exploration. It is a trial-and-error process!!
Chetty, R., et al. (2022). Social capital II: determinants of economic connectedness. Nature, 1-13.
What is the social capital that affecting economic mobility? Three types of social capital by ZIP (postal) code in the United States:
They find that the share of high-SES friends among individuals with low SES is among the strongest predictors of upward income mobility identified to date:
Differences in economic connectedness can explain well-known relationships between upward income mobility and racial segregation, poverty rates, and inequality
Maantay, J., & Ziegler, J. (2006). GIS for the Urban Environment. Redlands, CA: Esri Press.