To view a legend, choose Legend from the View menu, and choose the appropriate item (Overlay or Base) from the cascading menu.

First, let us discuss the window for the overlay legend. We will discuss the window for the base legend below.

The overlay legend is created when you add graphic characteristics specifications with the Description field filled in. If you've never filled in the Description field, you will have no overlay legend. (If you don't know how to add or edit graphic characteristics, see Edit Graphic Characteristics.)

For each graphic characteristics specification with a description, there will be one entry in the overlay legend. Entries for pointnodes will be at the top; entries for lines will be at the bottom.

On the left of each entry is a representation of the graphic characteristics that were set by the specification. On the right is the description.

When finished viewing the legend, you may click Close , or you may just move it out of the way and keep working.

Since only the specified graphic characteristics are shown, the question arises, "what if a label style is specified, but no label text?", or "what if a symbol/ring color is specified, but no symbol or ring?"

The answer to the first question: the word "Label" is displayed in the specified style.

The answer to the second question: a small rectangle is displayed in the specified color.

Otherwise, graphic characteristics that are not specified are displayed with default values in the legend. For instance, label text, bitmap symbols, rings, and lines are set to black unless another color is specified. Lines and rings are thin and solid unless specified otherwise.

Because the size of a ring will vary with the scale (except when using pixels to specify the radius), and will usually be different for each object (when the radius is set to an attribute field), no attempt is made to indicate the size of a ring. In the legend, a ring will always be just big enough to surround the label and/or symbol, if any.

Because the final graphic characteristics shown for each object are the cumulative result of all specifications that apply to it, you need not define a legend entry for each possible set of characteristics. You may treat each characteristic (e.g., line width, color, dash style) separately.

For instance, say you use line width to represent five different classes of road, from dirt roads to divided highways. Then you use color to represent four different levels of government that provide the funds for maintaining the roads, from local to federal government. And, finally, you use solid lines to represent existing roads, a dashed line to indicate roads under construction, and a dotted line to indicate proposed roads.

If you do the math (5 x 4 x 3) you can see that there are sixty possible combinations. (OK, granted, proposed federal dirt roads are probably pretty rare, but there are still a lot of valid possibilities here.) Do you want to create a specification and legend entry for each possible combination? You can if you want. But usually it makes sense to just create a specification for each individual characteristic. In this case, that would result in only a dozen specifications and entries in the legend.

Creating a good legend is not an exact science. For a simple map it will probably be simple. For a complex map it takes a bit of thought. Usually it is best to minimize the number of entries in the legend.

Here is an example of a legend from an index map which shows a grid of quadrangles and which of three themes are available for each. There are actually eight possible combinations of themes. So we could show all eight (i.e., "none", "Transportation", "Boundaries", "Transportation and Boundaries", etc.), but if we show only these three, folks should be able to figure out the other five.

Perhaps the best way to learn about overlay legend entries is to leave the window open and experiment by repeatedly editing one or more graphic characteristics specifications (with the Description field filled in).

Here is the window for the base legend. Entries for polygons are at the top; entries for lines are at the bottom. (This legend is bigger than its window, so you will need to use its scroll bar to see the whole thing.)

Unlike the entries for the overlay legend, the entries in the legend for the base map cannot be modified.

Copyright © 2005 by Dapper Mapper