A Map Primer

Maps are graphic representations of the real world. They are the main tool of geographers both for displaying spatial information that they might collect in the field or from existing literature (often converting data from tables such as those the US Bureau of the Census publishes) and as an analytical tool for discovering spatial patterns and relationships.

There are various types of maps running the gamut from highly precise depictions of the earth's surface to imaginary world-views that depict peoples' perceptions of the world around them.

Some of the different kinds of maps with which we will work are:

  1. Mental maps. Here a person drafts their view of a place or region from memory.
  2. Sketch maps. These are more or less abstractions of the real work whose main purpose is to highlight spatial relationships between places when there is no need to provide detailed or precise representations of the actual places involved.
  3. Reference maps. The main purpose of these maps is to show where things are located. The Virginia state highway map is an excellent example. Reference maps typically include mostly place names and symbols depicting towns, transportation routes, and/or county and state boundaries.
  4. Thematic maps. The main purpose of these maps is to point out spatial patterns for a given phenomenon or "theme." Pin-point precision is not necessary because you wouldn't use this type of map to actually locate a given place or even tell precisely what was the characteristic of a given place with respect to the phenomenon in question. These maps tend to be generalizations of the distribution of some facet of physical or cultural geography of interest to the map's author.

Maps are a graphic means of communication. As such they tell stories. A good map tells its story concisely and clearly. It is designed with its reader in mind as well as its message. It uses conventional symbols as its language.

All maps should contain the following elements:

 

Thematic Maps

All thematic maps consist of a base map (an outline of the area being mapped and any other references points or lines that will help orient the reader) and an overlay that depicts the distribution pattern of the phenomenon being mapped.

Different types of phenomena or data require different mapping techniques. The first distinction needs to made between qualitative and quantitative maps:

Qualitative maps show differences in the kind of things that are found in different regions. They answer the question "What?" For example, an agriculture map of Virginia would show that tobacco is the dominant commercial product of Southside, beef cattle the dominant commercial product of the Valley of Virginia, and so forth. The physiographic map of Virginia that you will be constructing is a qualitative thematic map because it is only telling that different kinds of surface configuration and subsurface geology occur in different regions of the state.

Quantitative maps on the other hand show differences in amount or degree of a given phenomenon. They answer the question, "how much?" Numerical data are the sources of information. These may be sums or totals, percents, means, medians, and so forth. The nature of the phenomena and how the data are collected-whether data are continuous or discrete-determine the best mapping method. For example, spatially continuous phenomena like precipitation amounts are mapped using isolines; total counts of population may be mapped using dots or graduated symbols; mean income on a county by county basis would use area symbols or choropleth mapping. We will work with each of these types in course assignments.

 

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Department of Geography, Radford University