Preparing map outlines for proper bit size

A couple of years ago I created a 2-foot-wide county-by-county wood map of Oregon. Took for freakin’ EVER to get the files right, so I haven’t done any more. There are county maps available for free, in vector, but they need to be revised so a 1/8" bit can fit everything together. Recently I wanted to do Washington state in the same scale, but didn’t want to spend aaaaaallllll that time redrawing it county by county. So I messed around in Illustrator and found a set of path operations that will smooth everything out with minimal fussing. This technique works for any interlocking irregular shapes, like maps, and I thought I’d share the formula. This is specific to Illustrator but I’m sure Inkscape can do the same thing. This is for a 1/8" bit (1/16" radius of .0625"), for other bit sizes change the radius number to half the width of the target bit.

How to smooth out interlocking shapes for 1/8" bit in Illustrator:

  1. Get vector closed shapes (e.g. map elements like countries, states, counties, etc.) and size appropriately
  2. Select a closed path
  3. Path → Offset Path → -.0625" (note the minus sign) (also note, Joins should be set to “Round” and not “Miter”)
  4. Stroke 9pt
  5. Path → Outline Stroke
  6. Path → Offset Path → .0625" (no minus sign)
  7. Right Click object → Release Compound Path, Delete Inner Path
  8. Path → Offset Path → -.0625" (again with the minus)
  9. Delete intermediary shapes and select the smooth one
  10. Place the new smoothed shape in place
  11. There may be small gaps where corners come together, which can be manually edited with the pen tool

It took probably 8-10 hours to draw Oregon’s 36 counties by hand, making sure to keep the inner and outer radii large enough for the selected bit. With this new technique - and an Illustrator Action macro - I converted Washington state’s 39 counties and tweaked the minor gaps in about half an hour. (Puget Sound islands took most of the tweak time.)

Now, I haven’t actually routed out the Washington pieces yet, but they should work fine, based on my Oregon routing.

I’m mostly posting this here for when I forget how to do this in 2 years when I tackle California. Hope somebody else finds it useful as well.


Thanks for this I appreciate your posting this information. I’ll post back if I can do this with Inkscape.