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I'd like to know some cartographic techniques to call out an inset map.

August 23 2007 | 0 comments
Categories: Map Elements, Page Layout

I'd like to know some cartographic techniques to call out an inset map. ArcMap has an option
to add a leader line from the inset map to the extent rectangle, but it looks terrible no matter how you symbolize a leader line. Any suggestions?

Mapping Center Answer:

Response #1:

I agree the leader line option at best falls into Tufte’s “Chart Junk” classification, and at worst interferes with the healthy functioning of your map. Thus, I would recommend making the outline prominent enough to be seen with out becoming the most important thing on the map. For instance, it could be red, but maybe not the brightest red (RGB: 235, 80,80), and a light weight of 2.0 points +/- 0.5. For maps with one inset that should be sufficient.

For maps with multiple insets that may also be the same shape or show areas that are close together, the convention I’ve seen and like is to label the insets A, B, C, D… and put the labels in one of the upper corners. Use the same color for the label text as is used for the extent rectangle frame. For that would be a manual process, but at 9.3 we’re adding options to the Maplex Label Engine to do that sort of labeling if you’ve got polygon features for each of your insets (that layer would exist in the main data frame and each of the inset data frames).

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Response #2:

Just to add a few comments -- I agree (above) that it is best to avoid the leader line approach -- it usually obscures portions of the larger map and more than that it is usually unnecessary for the map reader since he or she can usually form a visual association between eh main the map without it. To reinforce the associate (which is in effect what the leader line does), you can try a few cartographic tricks:

Use text to explain the association (small font, black or some not very prominent color) - e.g., “Area Shown at Left” or ”See area detail map at left” or “See enlargement below”. If there are multiple insets, something like suggested above (a, b, c, d) - but avoid using numbers unless you want the readers to actually look at the insets in a particular order.
Use the same border on the map as you do around the inset.
Slightly superimpose the inset over a small and irrelevant part of the main map.

These tricks will help create that visual association -- and keep the “chart junk” (a short discussion came up about this on the Cartography Forum) to a minimum.

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