Old maps

Import a scan of a plat map, county atlas or old topo and line it up with today’s map by matching a few landmarks. It then sits right on top, with your position on it.

Adding a map

1. On the Old maps tab, tap + Add map.
2. Choose From Photos, From Files (JPEG or PNG), or Take a photo of a paper map.
3. Give it a name, such as “1875 Licking County atlas”.
4. The app prepares it (cutting it into tiles so it stays sharp when you zoom), then opens the line-up screen.

Tip Scans up to about 220 megapixels work. Higher-resolution scans give a sharper overlay; photographs of paper maps work too, but hold the phone flat and square to the page.

Lining it up

The line-up screen shows the old map on top and today’s map below, each with a crosshair. You’ll mark the same spots on both. Each matching pair is an anchor.

1. Pick a landmark that hasn’t moved: a road crossing, a church, a bridge, a creek crossing, a section corner.
2. Move the old map so its crosshair sits exactly on it.
3. Move today’s map so its crosshair sits on the same place. Search and the satellite/topo switch help here.
4. Tap + Anchor.
5. Repeat across the whole sheet: near each corner and through the middle.
6. Tap Done. The app builds the overlay and opens it on the Map tab.

Two anchors are enough for a well-surveyed map. Old hand-drawn maps need many more, spread across the sheet, because their errors vary from place to place. With three or more, the map is stretched locally between anchors, like a rubber sheet, so each area lines up on its own.

Checking your anchors

• Green: agrees with its neighbours.
• Yellow: worth a second look.
• Red: probably the wrong landmark, or the two crosshairs weren’t on the same spot.

Tap List to see each anchor’s error in feet or meters. Select one to Move or Delete it. On iPhone, Mesh shows the triangles between anchors; red ones are folded, which means two anchors cross over each other.

Using it

On the Map tab, tap the old map name at the top to switch maps or turn it off. In Overlay, the Strength slider in the same place fades it in and out. To fix anchors later, use Line up next to the map on the Old maps tab.