# Projections

Pick a projection to morph the same ETOPO1 terrain into it. Drag to orbit the globe or pan a flat map.

## Choose a projection

```ts
import {
  glyphMapGlobe, glyphMapEquirectangular,
  glyphMapMercator, glyphMapOrthographic,
} from "@glyphcss/maps";

const projection = glyphMapGlobe({ radius: 1, exaggeration: 24 });
glyphMapEquirectangular({ exaggeration: 24 });
glyphMapMercator({ maxLat: 85.05112877980659, exaggeration: 24 });
glyphMapOrthographic({ lon0: 0, lat0: 0, exaggeration: 24 });
```

| Projection | Use | Defaults / limits |
|---|---|---|
| `glyphMapGlobe` | Orbit a sphere | `radius: 1`; far hemisphere hidden |
| `glyphMapEquirectangular` | Flat longitude/latitude map | Full world |
| `glyphMapMercator` | Flat map with enlarged polar regions | `maxLat: 85.05112877980659`; poles excluded |
| `glyphMapOrthographic` | Fixed hemisphere on a flat disc | `lon0: 0`, `lat0: 0`; far hemisphere excluded |

All options are optional. `exaggeration` defaults to `1` (true-scale relief); `24` makes terrain easier to see. Built-in building extrusions keep true-metre heights regardless of exaggeration.

## Custom projections

```ts
import { geoMollweideRaw } from "d3-geo-projection";
import { glyphMapFromD3Raw } from "@glyphcss/maps";

const mollweide = glyphMapFromD3Raw(geoMollweideRaw, { exaggeration: 24 });
```

Install `d3-geo-projection` separately. The adapter accepts `id`, `domain`, and `exaggeration`; defaults are `"glyph-map-d3-raw"`, the full world, and `1`. The raw projection needs `.invert` for unprojection; otherwise `unproject` throws `TypeError`.

For your own `GlyphMapProjection`, supply `id`, `domain`, `exaggeration`, `project(lon, lat, elev)`, and `unproject(world)`. Coordinates use degrees; elevation uses metres. Return non-finite coordinates outside the domain. Optional `visible`, `cameraForCenter`, and `centerForCamera` support hemisphere visibility and orbit navigation.

## Animated transitions

```ts
await map.setProjection(glyphMapGlobe({ exaggeration: 24 }), { durationMs: 900 });
```

The current centre stays anchored. Use `durationMs: 0` for an immediate change. Changing projection leaves [walk mode](/maps/camera/#street-level-walk-mode).