How it works, once a week:

1. About 700,000 active U.S. listings come in from a licensed listings API.

2. Each listing near public land gets its county parcel boundary, from state and county GIS services where they publish them and from a licensed parcel provider elsewhere. With no boundary, the page says so and measures from the listing point, but never claims a shared edge.

3. Public land is USGS PAD-US 4.1, narrowed to land an agency actually owns (Category = Fee, so no conservation easements), that's open to the public, and that's at least 50 acres.

4. Parcel and public land are compared in a local metric projection (shapely/geopandas): within (an inholding), bordering (the boundaries touch, and the shared edge is measured in feet), or adjacent (within 75 m, about a road's width).

Each property also gets the size of the connected public land behind it, its elevation (USGS 3DEP), road access (Census TIGER roads), FEMA flood zone and Forest Service wildfire hazard. The output is about 16,000 static pages with Leaflet maps on Cloudflare Pages, rebuilt every Monday on a Mac mini. ZIP search looks the ZIP up in your browser from Census centroids, so nothing you type is sent anywhere.

Things that were harder than expected:

- Lot sizes sometimes arrive in square feet in the acres field. A Birmingham, AL listing came through at 7,000 acres. Sizes are now checked against price, property type and the parcel itself, and corrected or withheld with a note.

- Condo and subdivision listings often resolve to the association's common tract, so a single town lot can appear to share miles of boundary. Those are flagged as shared parcels.

- PAD-US stores some units as one multipart polygon. My first "connected public land" figure for one Montana property was 69.7 million acres, about three-quarters of the state. Units are now split into pieces and joined only where they actually touch.

- Road centerlines and lot lines come from different agencies and are often tens of meters apart, so "does a road touch this parcel" needs a tolerance, and frontage only counts where the boundary runs along the road.

It's free, with no account and no cookies. There are free weekly email alerts for any search, starting Monday. I'd especially like to hear from anyone who has bought rural land: what should it measure that it doesn't?

Really curious about your data sources. Where are you getting all this stuff?

Sure, there's the ability to hike directly from your home, but I imagine you'll regularly have people wander on to your property. And if something illegal happens on your property by a different party, you might be liable.

Seems like the cons outweigh the pros. Or is there something I'm missing?

I live next to a State Park. It sounded really cool when I bought the house. No neighbors! Privacy! There is a trail accessible from my properly that goes into some woods, which you only want to be in during the Fall / Spring because the ticks and chiggers are intense.

The biggest issue with sharing a border with the state is the fence line. Technically it's on them to maintain. The woods are filled with mostly 200 foot trees. They exist right up to my property and fall every year during big storms. There goes the fence line. I have dogs so the fence is important. Otherwise they run out into the woods that have licensed bow-hunting during the Winter.

In practice its impossible to get the fence fixed. You are working through layers of bureaucracy and mismanagement. There is no vested interest from a parks service to work well with hundreds of neighbors individually. I'd build fence lines myself, and could easily pay for it, but it's the upkeep of those fences that would be difficult because so many trees (really, it's every year) fall down from their side.

My main point is that sharing a properly line with the government is more like sharing a properly line with nobody. You may as well own that land. Don't expect any upkeep and go in with eyes open.

When I look for a parcel of land, I'm also interested in proximity to healthcare, groceries, airports (bad!), motor sports, shooting ranges; general steepness of the property particularly at the roadway (too steep makes the property unusable), topography in general (any flat spots to build a house?); availability of power; water features; bikability (checked by looking at Strava's heatmap); average number of days temperature > 85F; average number of days temperature < 30F. There's more but this list is long enough already.