# DEM Document

## Purpose
Digital Elevation Model tiles or mosaics for terrain rendering and processing.

## GeoJSON (DB metadata)
```json
{
  "type": "Feature",
  "geometry": {"type": "Polygon", "coordinates": [[[
    30.10, 59.90
  ], [
    30.20, 59.90
  ], [
    30.20, 60.00
  ], [
    30.10, 60.00
  ], [
    30.10, 59.90
  ]]]},
  "properties": {
    "type": "DEM",
    "title": "WorldDEM 30m",
    "created_at": "2025-07-01T00:00:00Z",
    "updated_at": "2025-07-01T00:00:00Z",
    "source": {
      "url": "/tiler/tiles/{z}/{x}/{y}@2x",
      "type": "Raster",
      "url_params": {
        "url": "s3://<bucket>/<ResultKey>/<filename>"
      }
    },
    "metadata": {"resolution": 30, "units": "meters", "vertical_datum": "EGM96"}
  }
}
```

## Required properties
- `properties.type` = `DEM`
- Polygon footprint of the tile or mosaic extent
- Correct height units and vertical datum in `metadata`

## Publishing workflow
1. Produce DEM tile or mosaic in GeoTIFF (COG preferred).
2. Upload to storage and record its URL.
3. Publish Feature with type `DEM` referencing raster.

## Validation checklist
- Nodata value set and overviews present (for COG).
- Heights in expected units and datum.
- Footprint matches raster extent.

See [Common properties](../common.md) for shared fields like legend, metadata, and classification.
See also: [GeoJSON Strategy](../../Geojson_strategy.md) and [Upload Strategy](../../Upload_strategy.md).