Rock Climbing Map Tip 1: Removing overlap in Illustrator without removing polygons

…or When transparency matters!

This is a first in a short series of posts demonstrating some of the aesthetic design choices and mapping methods (including Adobe Illustrator tips) that I used while making this monochrome Three. Two. One. Climb on, Vancouver! rock climbing map centered around southwest British Columbia and northwest Washington state. The map shows how far a person can drive from the heart of Vancouver, B.C. in one, two, and three hours.

What it’s all about

There’s no simple phrase to sum up what this post is about, even though the method is straightforward. Essentially, sometimes your map has overlapping polygons that both sit on top of other map data that needs to be visible as well. So the overlapping polygons need a level of transparency. But the overlapping nature of the polygons causes the overlapping area to be too opaque. So, you need to remove the overlap while also keeping the polygons. This post is about that.

Three. Two. One. Climb on, Vancouver rock climbing map, full view
Three. Two. One. Climb on, Vancouver rock climbing map, full view

Dealing with Overlapping Transparent Polygons in Illustrator

Naturally, the one-, two-, and three-hour drive-time polygons (closed paths in .AI speak) that all radiate from the same Vancouver, B.C. point will overlap with one another. The three-hour polygon will be the largest, and the two-hour will be encompassed with it. Likewise, the one-hour polygon will be encompassed in both the two- and three-hour areas. This concentric situation is depicted as simple circles in map’s legend below (Estimated Drive Time).

Vancouver Rock Climbing Map Legend only
Climbing map legend

For this monochrome map, I also wanted these drive-time polygons be transparent so that the hillshade and other map data beneath these polygons would be visible. But, I didn’t want the overlapping areas to become more opaque simply because they were overlapping. For this reason, I needed to “punch out” the overlapping areas to create holes inside the encompassing polygons. For example, each of the rectangles in the sample map below have the same red hue. It is the opacity difference in each polygon that makes them appear as a gradient of color (35%, 50%, and 75%). Due to their overlap, it much easier to see the map data beneath the outermost rectangle than it is to see the data beneath the center rectangle. That is, in part, because the overlap makes the center rectangle much more opaque than what I set it to be. So, let’s take a look at how to punch out some holes with the Minus Front Pathfinder tool. These are the same steps I followed for the drive-time polygons on the Vancouver rock climbing map. After performing these steps on the sample map (as well as , the actual set transparency will be true for all of the polygons, not just the outermost one. I’m going to share the steps I do to accomplish this, as well as the sample .AI file for anyone who wants to practice this Illustrator mapping method. You can download that .AI file here:

Overlapping concentric rectangles prior to applying the Minus Front tool
Overlapping concentric rectangles on the sample map prior to applying the Minus Front tool

For my Vancouver climbing map and this sample map, punching out areas within the drive time polygons are somewhat straightforward. However, this method can be extended to more complicated maps with multiple holes that need to be punched out. I find myself frequently applying this method on maps where a government land polygon has either glaciers or additional jurisdictions within it, like this Mount Baker area map. Because the hillshade needs to appear the same beneath the glaciers, the Wilderness, and the national forests and parks, the Minus Front tool can be quite useful.

Here’s how to make those shapes.

  1. Open the Pathfinder Window. Open the Pathfinder window if it is not already open. Window –> Pathfinder
  2. Copy and Paste the “puncher” shape. Copy the second-most-outer rectangle (CTRL +C), and then paste the copy in front in place so that it sits exactly where the original rectangle sits. In Illustrator, you can do this with CTRL + F (paste in Front), or you can go Edit -> Paste in front. After pasting the copy in front, you will now have two second-most-outer polygons. Note that if you were just subtracting a shape from a polygon without needing to keep a copy, you wouldn’t need to do this copy step. But we need all three of these rectangles to be visible on the map.
  3. Select the “punching” shape and the to-be “punched” shape. If you’ve done nothing with your mouse or keyboard since CTRL +F, then the copied polygon should still be selected. If it isn’t, then make sure that it is. Then, holding the Shift key, select the outermost rectangle so that just the copied polygon and the outermost polygon are selected.
  4. Minus Front! With both of those two polygons selected, go to the Pathfinder window, and click the Minus Front tool (pictured below). This will subtract whichever shape is selected and in front from the shape selected and beneath.

Notice that the copied polygon you pasted in step 2 is invisible now. That is because it is being used to make a Compound Path. Since you made a copy of the second-most-outer polygon, the original one is still there. To continue, you can subtract the shape of the center rectangle from the second-most

The Minus Front pathfinder tool in Illustrator
The Minus Front pathfinder tool in Illustrator

Below is the sample map after applying the above steps. You can see the buildings, streets, and other map data beneath overlapping areas much easier now.

Sample Map after applying Minus Front tool
Sample Map after applying Minus Front tool

Here is how those polygons appear if I separate them. Because the outermost and second-most-outer rectangles are Compound Paths, to remove these donut holes, you would select the shape, and then Object –> Compound Path –> Release. Note that this will also reveal that hidden copied rectangle. You can just select that rectangle and delete it.

Each of the concentric rectangles after applying the Minus Front steps (spread out for illustration).
Each of the concentric rectangles after applying the Minus Front steps (spread out for illustration).

There are a couple more tips I’d like to share from this monochrome rock climbing map which have more to do with color choices. I look forward to sharing those soon!

Keep on mapping!


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