Coordinate systems
Mapplic positions everything in a normalized coordinate space, but it can also accept real-world latitude and longitude. This page explains the two systems and how geocalibration bridges them.
Two ways to place a location
| System | Field | Looks like | When to use |
|---|---|---|---|
| Normalized | coord | [0.5, 0.42] | The default — a fraction of the map’s width and height. |
| Geographic | latlon | [40.71, -74.0] | Real-world latitude/longitude on a geocalibrated map. |
Normalized coord is the canonical system. [0, 0] is the top-left corner and
[1, 1] is the bottom-right, so [0.5, 0.5] is the exact center.
Geographic latlon lets you position locations by GPS coordinates, which is handy
when your data already comes with lat/lon — store locators, regional maps, imported
datasets.
Geocalibration
Geographic coordinates can’t be drawn directly; they have to be projected into the normalized space first. Geocalibration is the configuration that makes that projection possible. It needs two things, set in the Layers panel:
| Setting | Key | Description |
|---|---|---|
| Geocalibration | geo | Turns geographic positioning on. |
| Extent | extent | The map’s geographic bounds, as [minLon, minLat, maxLon, maxLat]. |
The extent is the bounding box of the map image in real-world coordinates — the
longitude and latitude of its left, bottom, right, and top edges. Once Mapplic knows
that box, it can place any latlon that falls inside it.
How the projection works
Mapplic uses the Web Mercator projection (EPSG:3857) — the same projection as Google Maps and OpenStreetMap — so a map exported from standard GIS tooling lines up. Conceptually:
- Longitude → x is a straight linear mapping across the extent’s width.
- Latitude → y is logarithmic, because Mercator stretches space progressively toward the poles.
The result is a normalized [x, y] in the same 0..1 space as a hand-placed coord.
When both are present, an explicit coord wins. Mapplic resolves a location’s position
in this order: a manually set coord, then an editor-estimated position, then the
projected latlon. Enable geo, set a valid extent, and leave coord empty for the
latlon to take over.
Producing an accurate extent for a custom image is a GIS task that demands precise bounds. The built-in geographic maps already ship geocalibrated.
Configure geocalibration in the Layers guide. The
coord and latlon fields are documented in the
Map data schema, and geo and extent under
Layers and map settings.