Map legend

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Legend.gif
Map legend.png

A map legend or key is a visual explanation of the symbols used on the map. It typically includes a sample of each symbol (point, line, or area), and a short description of what the symbol means. For example, a short segment of a blue sinuous line may be labeled 'rivers'. [1] Because map symbols’ meanings vary from region to region, a clear and concise legend is critical for conveying the distinctive characteristics of the map. [2]

The legend is a graphical representation of information, with design principles similar to a map or any other graphic. The only difference is that it is related to the information on the map it is connected to. Therefore, it is important to remember the layout design concepts such as harmony, visual balance, clarity, visual logic, logical groupings, and unambiguous references to create a legend that is effective in relationship to the map. Creating a well laid out legend will enhance the overall gestalt of the maps visual appearance.

The legend should be simple and its position largely depends on the open space available in the map; a legend should be centered in an area of open space. It should be large enough that it is legible but small enough to stay low in the visual hierarchy.[3]

Considerations in Legend Design

The legend is key here in order to understand the data that is being presented on the choropleth map. The legend, however, is very large and can be very distracting. It is able to fulfill its purpose of informing what the different colors mean, but it is higher on the visual hierarchy that the actual geographic area being looked at.
  • Content is what is contained in the legend to aid in the interpretation of the map. Legends usually contain a title and portray the symbology with a concise explanation. The title of the legend does not need to have the word "legend" in it; often it does not need a title at all. However, when it is necessary (i.e. to explain the meaning of the choropleth map or other vital information in the legend) then the title becomes the key element. The symbology within the legend will contain figures, shapes, lines and colors. If symbols on the map are self-explanatory, they need not appear on the legend. [4] Whenever a legend involves quantities of any type, explicitly state the units on the legend. [5]
  • Design involves the overall appearance of the legend. The symbology of the legend must match the symbology on the map with the same size, weight, color and meaning. If the symbology is difficult or slightly confusing, it is important to have a brief explanation of the symbol so the reader of the map understands the meaning. A highly aesthetic legend can be nice yet distracting from the map. Be concise - not every symbol used on the map needs to be in the legend. In choropleth mapping, for example, orientation is an important aspect of legend design and there are many arguments about the benefits and detriments of vertical versus horizontal legends[6]. The main task of both orientations is to accurately and effectively depict more or less of a certain value or phenomena. Ultimately, most legend layout conundrums are decided by available space on the map.
  • Placement is where the legend itself is located on the map. Some places are better than others. Keep in mind that the legend is not the main attraction--it is used to describe the main attraction. The size should only be large enough to be legible for the reader. [7] It is best to place the legend in an area of open space on the map [8]. For example, placing a legend over the Pacific Ocean, instead of over a country or state, for a political map of the world would be a much cleaner view.

Legend Properties in ArcGIS Pro

LegendProperties.png

Once a legend is inserted in the layout, it is possible to access and edit the legend properties. Some of the elements available for the users to modify are: Background, border, shadow, tittle, group layer name, headings, labels and descriptions. Within those elements it is possible to modify and change the size, spacing or color of the font, adjust columns and frame and modify border width and color between others.[9].


Notes

  1. ArcGIS 10 Help, "Working with legends." Accessed 27 September 2012
  2. Cartography Design. Accessed: October 1, 2012. "
  3. Slocum, Terry; McMaster, Robert; Kessler, Fritz; Howard, Hugh. Thematic Cartography and Geovisualization (Third Edition). 2009 Pearson Education, Inc.
  4. "Elements of Cartographic Style"
  5. "Elements of Cartographic Style"
  6. Slocum, T. A. et al. (2009). Thematic Cartography and Geovisualization(3rd ed.) Upper Saddle River, NJ: Pearson Prentice Hall.
  7. Keith C. Clarke. Thematic Cartography and Geovisualization
  8. Keith C. Clarke. Thematic Cartography and Geovisualization
  9. http://pro.arcgis.com/en/pro-app/help/layouts/work-with-a-legend.htm