A scale bar is a graphical means of depicting distance on a map. In cartographic design, scale bars are unique to the designs and purposes of the map; consequently, they vary in size, design, ratio, and units of measurement. They are useful if a map is used in determining distance.
The two other means of representing distance on maps, representative fractions and verbal scales, become inaccurate if the map is stretched or shrunk. Scale Bars, on the other hand, enlarge or shrink with the map itself. This enables it to stay true to scale and provide a way to make accurate measurements.
It is important to know who the audience is before choosing a scale and corresponding scale bar. Different groups use different types of scale bars. Engineers, for example, tend to have a set of scales that they use and it would be important to follow their guidelines. However, if there is a large scale map for a neighborhood brochure showing the location of a new park within that neighborhood, there may be no need for a scale bar.
Overall, maps that are going to be repeatedly expanded or diminished should always use a scale bar. This includes occasions when the map is going to be displayed on a projector or computer screen. Whenever maps are displayed electronically, it is best to use a scale bar.
Styles and Design
There are many different styles of scale bars/lines that can be used in maps. Some include:
- Simple scale lines
- Stepped scale lines
- Alternating scale bars
- Single division scale bars
- Hollow scale bars
Scale bars can also be formatted to meet the needs of the map's audience and make them more visually appealing. Depending on the scale and audience, the scale bar's distances can be measured in miles, yards, feet, kilometers, meters, and more. The subdivision frequency and distance between subdivisions within the scale bar can also be altered to make the scale bar more practical and less overwhelming. The color of the scale bar or line can also be changed to lower the scale bar in the visual hierarchy of the map. The key is to remember your audience and scale when formatting your scale bar.
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- Parmenter, Barbara. “Creating and Editing Scale Bars and Legends.” Tufts University GIS Center, 9 Sept. 2014.
- “Scale Bars.” ArcGIS Pro, ESRI, pro.arcgis.com/en/pro-app/help/layouts/scale-bars.htm.