I want to do a few tiny mapping projects in Maine, because I have some local knowledge, and I know people there who need maps. But I’ve run into a number of issues, and it has been suggested that I should write these up for a larger audience.

County borders

The county borders in Maine are wildly inaccurate, at least along the coast. They’re based on a low-res trace of the shoreline, which has several problems:

1. You get a lot of cluttered borders deep within a county.
2. The borders swerve randomly all over coastal islands. This is ugly, and incorrect.
3. Many smaller islands are omitted entirely.

Here’s a sample. Every piece of land on this map actually falls within the county line, and I’d imagine that the ocean is under county jurisdiction as well:

Now, we actually have pretty accurate county data in various GNIS and TIGER fields, if we know how to interpret it. Let’s set up a JSOM filter to exclude everything but Lincoln county data and the border line:

-("gnis:county_id"="015" | "gnis:County_num"="015" | "tiger:county" = "Lincoln, ME" | border_type = "county") 

This gives us a pretty decent county boundary:

You can see where I started cleaning up the county borders by hand on the left side of the map, relying on GNIS county data on the mid-river islands to get it approximately right.

We either need to find a better data source, or we need to redraw the county lines using GNIS/TIGER data. Even rough, hand-drawn county lines would be more accurate than what we have now.

Nominatim and town lines

Here’s another map. Everything on this map should have “addr:city=Boothbay”. But as you can see, the actual town of Boothbay is marked using a point:

The problem arises because of “Trevett”. This is local Boothbay post office, not a real town. But Nominatim has decided that many roads are in “Trevett”, and it can’t find them if you search for the actual postal addresses that use “Boothbay.”

When you combine the lack of town lines with the bad county lines, OpenStreetMap won’t be able to locate the home addresses for people who live near the Maine coast. And this will make it hard to enlist contributors in these areas: We need a certain minimum level of usability before people will try to suggest improvements.

So what do people think? Is it better to have dodgy hand-drawn borders than what we have now? Or should we find a better data source? And if so, where?