Maps are the primary tools by which spatial relationships are visualized. Maps therefore become important documents. There are several key elements that should be included each time a map is created in order to aid the viewer in understanding the communications of that map and to document the source of the geographic information used.
Numbered below are decriptions of cartographic elements that are commonly found on a map layout.
1. Data Frame
The data frame is the portion of the map that displays the data layers. This section is the most important and central focus of the map document. In the example displayed at the end of this article, the data frame contains fire history for the community of Topanga.
The legend serves as the decoder for the symbology in the data frame. Therefore, it is also commonly known as the key. Descriptions detailing any color schemata, symbology or categorization is explained here. In the legend below, the fire history schemata has been categorized with a graduating color scheme. The legend details which colors refer to which years. Without the legend, the color scheme on the map would make no sense to the viewer. The legend tells the viewer that the lighter the color, the longer the last recorded date of fire has been.
The title is important because it instantly gives the viewer a succinct description of the subject matter of the map. The title “Fire History in Topanga, California” quickly tells the viewer the subject matter and location of the data.
4. North Arrow
The purpose of the north arrow is for orientation. This allows the viewer to determine the direction of the map as it relates to due north. Most maps tend to be oriented so that due north faces the top of the page. There are exceptions to this and having the north arrow allows the viewer to know which direction the data is oriented. To learn more about when to use a North Arrow, read “To North Arrow or Not to North Arrow“.
The scale explains the relationship of the data frame extent to the real world. The description is a ratio. This can be shown either as a unit to unit or as one measurement to another measurement. Therefore a scale showing a 1:10,000 scale means that every one paper map unit represents 10,000 real world units. For example 1:10,000 in inches means that a measurement of one inch on the map equals 10,000 inches in real life. The second method of depicting scale is a comparison with different unit types. For example, 1″:100′ means that every inch measure on the paper map represents 100 feet in the real world. This ratio is the same as 1:1200 (1 foot = 12 inches). In addition to text representation as described above, the ratio can be shown graphically in the form of a scale bar. Maps that are not to scale tend have have a “N.T.S” notation which stands for “Not to scale.”
The citation portion of a map constitutes the metadata of the map. This is the area where explanatory data about the data sources and currency, projection information and any caveats are placed. In the example below, the citation tells the source and date of the data. Citations help the viewer determine the use of the map for their own purposes.
Other elements such as a border (7) and inset map (8) can be placed on the map to further aid the viewer.
Article first written: January 23, 2000. Last Updated: September 13, 2011.