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Comment by codingdave | Hacker News Reader

> I set up an experiment that compares the original geometry with the simplified geometry by testing 1,000,000 random points within the US.

I'd be curious if the reliability is different if, instead of random locations, you limited it to locations with some level of population density. Because a lot of the USA is rural, so that random set is not going to correlate well to where people actually are. It probably matters more the farther east you go as well, as the population centers overlap borders more when you get to the eastern seaboard.

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Good thinking. I discuss population density, cities near borders, and narrow borders in the last section.

As a native Philadelphian, I immediately see why you need a good resolution here - at 0.1 degrees resolution you very well could have assigned my birthplace to New Jersey. If I'm not mistaken New York and Philadelphia are the largest cities where you might have a problem. Chicago's on a state line but the Illinois-Indiana border is straight.

I wonder if it’s actually straight though? In the chart on the page, Colorado is described as having 7000-something vertices, where I would have expected it to have … 4.

There's the congresionally approved boundary. Then there's the surveyed boundary. Wherein a team of people goes out and hammers survey marks and tags into the earth or creates man made monuments when that is not possible.

Another possible suggestion. Maybe choose random points that are within a set radius of points chosen along the borders? So perhaps choose first a random selection of points on the border, then choose random points within a circle (or perhaps just a square with a set delta in the lat/long) that are "nearby to the border" - then measure your error rates for those points at various boundary simplification tolerances? That'd remove the "middle of the state" random points where the border tolerance inevitable makes no difference.

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