Using Highway Shields as Legend Symbology-Is this possible?
On the maps that I produce it is much more important to explain what type of highway the different shields stand for rather than using the roadway symbology.
For example, I use an oval for State highways, a rectangle for Texas Farm-to-Market roads, a customized shield for toll roads, a pentagon shape for park roads and the traditional shields for Interstate and US highways. In addition there are several subsets of these categories such as business routes, loops and spurs.
The symbology is the same (a solid black line) for US, State and FM roadways with only a small difference in the width. I want the user to be able to look at the legend and match it to the roadway he is interested in because there will often be roadways that have the same number, but are of different types.
For example, SH 322 & FM 322 or US 259 & BU 259 or SL 7 (state loop)and SH 7 where, in this last example, the roadways would have the same width.
Mapping Center Answer:
Definitely possible to do, and in fact it's a preferred option. Just to explain this, because anyone new to symbolizing roads on medium to large scale maps will be confronted with this issue; you are symbolizing roads based on class, which has to do with carrying capacity, e.g., number of lanes, whether there is a shoulder, or whether access is restricted. You are labeling roads based on type, e.g., Interstate, U.S. Route, State Route, County Route, etc. (essentially how is the road funded).
Because each class of road could potentially be one of several different types, for instance a divided, restricted access highway may be an interstate or a U.S. Route, creating a much larger than is practical set of unique combinations of road class and road type for a legend.
Thus, the legend should have a unique entry for each road class, and then you will need to manually add a marker symbol for each type of shield that may occur on that class. You don't need to add all the dual use shields though, the idea with the legend is just to show the kinds of combinations that can happen.
The way I've usually done such a legend is to first add the layer with the symbolized road classes to the legend. Then manually add the marker symbols of the appropriate road types. To complete the picture, I also add text elements with just one number that occurs within the map or series to make it look real.
It's also useful to have a look at some published state road maps or road atlases to see how they configured their legend. A good bit of thought usually has gone into determining how to communicate the most while occupying the least amount of space.
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