How do we know exactly where we are? How do we represent our world? Cartography is the science of map making. Maps are representations of the world, usually two-dimensional, graphic relationships that use lines, symbols and colors to convey information or ideas about spatial relationships. Geographers use maps for four reasons:
- To locate phenomena- such as places, disease, peoples, etc.
- To show relationships - using maps to prove that some traits are correlated, such as population growth and infant mortality rates, or air pollution and auto usage.
- To prove ideas - maps illustrate relationships (as mentioned above) and statistics which allow us to support our ideas with location examples
- To ask questions - at times maps may reflect areas of contradiction from basic relationships. Such anomalies enable us to question the causal factors we are addressing.
These are four thematic maps of the United States. Each communicates different information, each could be used for different purposes. The most familiar maps are a combination choropleth (where colors have values) and vector (line) maps. Your standard road atlas is also usually a combination choropleth and vector map, where colors represent land cover (green for forested areas, blue for water, and sometimes yellow for urban areas), and roads are represented by lines. A third type of map is an isopleth map, where lines represent changes of a continuous value. A USGS topographic map is an example of an isopleth map.
In a standard choropleth map, the colors represent value added by manufacture. This is a graduated color scheme, commonly used to convey a range of values. Without even looking at the legend in this graduated color scheme choropleth map, you can probably figure out that the darker colors (reds and dark oranges) represent high values, and the lighter colors represented lower values.
Another type of map uses pie charts to convey labor structures. While the divisions of the pie chart represent the types of labor in each city, the size of the pie chart represents the total size of the labor force. In this way, the map is conveying both the distribution of the labor force by type and also by size. Such a map would answer questions like: Where is the majority of the labor force in the US located? Where is the labor force not located? What reasons can you think of for this distribution? These are the types of questions that a good map should prompt you to contemplate.
Browse through more examples of maps.
K. Allison Lenkeit-Meezan (Foothill College)