The legend is a standard element on most layouts. It provides the color and symbol key look-up details for the map element. It is comprised of items (icons, points, lines, polygons) and their associated labels (descriptions of the items). If the layout is being created for a narrow audience, such as your workgroup, and the map includes commonly understood feature types with standard symbology such as county boundaries, water bodies, elevation, and so on, then these may be granted an exception from inclusion in a legend. Wider audience maps may also exclude certain given feature types drawn with standard symbology such as blue water bodies or green land expanses; however, these are left to the discretion of the map author. Only exclude map layers from a legend—or the legend itself from the layout—purposefully. Don’t just forget some! Err on the side of the more legend items the better since a map is not worth much if its features cannot be understood. What is obvious to the map author can easily be unknown to the map viewer.
In some situations the entire legend could conceivably be omitted. For example, a map layout on a slide doesn’t need them due to the fact that the presenter will be talking about the slides and can point out the necessary features. Legends are also often unreadable on slides presented to a large audience. Be cautioned, though, that many slides are reproduced online or in other media, and these will need legends, especially when they are not accompanied by the presenter’s notes. Another situation in which you could omit a legend is when you are creating report maps that comprise a series of similar features. In this case, one legend at the beginning of the series can apply to all the maps and thus allow more space for the map elements on the subsequent pages. Simple, small, report maps may also have so few features that they only need to be explained in the text of the report or in the map captions. Exceptions also include basic basemaps with standard symbols or interactive maps that are well annotated or utilize click and hover techniques for point and area-based data.
Best practices: Items look best when placed to the left of their corresponding label. Complicated legends with many items necessitate grouping levels.
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The two forms of grouping levels most commonly seen are the categorical group (e.g., all land-use colors placed separately from all stream-level colors) and the shape-type group (e.g., all polygon features placed separately from all line features). Use headings to describe each group in categorically separated legends, if your organization schema is not immediately obvious. When categorical separations are not needed, shape-type groupings are often displayed in the following order: points, lines, polygons. Other times they are displayed in the order of relevance to the overall map purpose.
Default legends produced in the GIS are a great way to begin production of the legend but ought to be further manipulated prior to map publication. First of all, make sure there isn’t too much space between the items and their labels. Also, if the legend is describing a gradient of values (choropleth color scheme), then those items will look more professional if they are touching each other rather than separated by white space. Don’t forget that color gradients can be depicted vertically (Figure 3.4) or horizontally (Figure 3.5).
A label can still be associated with each item, although in many cases we can do without the intermediates and label only the maximum and minimum values. Creative color gradient legends could also employ other effects such as dials (e.g., speedometer-type dials) or graphs (e.g., elevations and colors).