# Actueel Hoogtebestand Nederland (AHN, national elevation model)

The elevation map of the Netherlands, measured by laser from an aircraft: at least ten measurements per square metre. There are two maps. The terrain model (DTM) is the bare ground. The surface model (DSM) is everything on it, including buildings and trees. Via PDOK as a map layer (WMS), as a raster API (WCS) and as a download.

- Publisher: Het Waterschapshuis, Rijkswaterstaat, Publieke Dienstverlening Op de Kaart
- Area: Netherlands · Finest detail: 0.5 metre
- Period: AHN4 (2020–2022) via PDOK; AHN6 deels (2025) via ahn.nl · Refreshed: every few years
- Access: Open · Licence: CC0 (AHN4 via PDOK); CC BY 4.0 (AHN6)
- Join keys: RD-coördinaten (EPSG:28992), kaartbladnummer
- Status: ok (2023-04-12) · PDOK-dienst met AHN4 (DTM en DSM 0,5 m)
- URL: https://www.ahn.nl

## What can you do with it?
- **How high is your street?.** Request the elevation at one point from the terrain model. You get metres relative to NAP. Line up a set of addresses and you see which neighbourhood lies below sea level.
- **Measuring buildings without a tape.** Subtract the ground from the surface (DSM minus DTM). What remains is the height of buildings, trees and bridges.
- **How much of the neighbourhood lies below NAP?.** Clip the terrain model to the neighbourhood boundaries and count the share of cells below 0 metres per neighbourhood. Leave out buildings and water, they have no value in the DTM.
- **Is the ground sinking?.** Compare two versions of the AHN at the same spot, for example in the peat meadow area. Note: since AHN5 the model is calculated differently, so preferably compare the new 1 by 1 kilometre tiles, which were re-derived for all versions.

## How to process it
1. **Elevation at one point.** A WMS GetFeatureInfo on the dtm_05m layer returns the elevation in metres relative to NAP as JSON (value_list). Use RD coordinates. With a very small bbox (2 by 2 metres) we got an empty response; with 200 by 200 metres and the click in the centre it works.
   `https://service.pdok.nl/rws/ahn/wms/v1_0?service=WMS&version=1.3.0&request=GetFeatureInfo&layers=dtm_05m&query_layers=dtm_05m&styles=&crs=EPSG:28992&bbox=121300,487300,121500,487500&width=200&height=200&i=100&j=100&info_format=application/json`
2. **A small piece of raster.** WCS GetCoverage cuts out a rectangle. 20 by 20 metres gives a GeoTIFF of 40 by 40 cells (float32, just over 3 KB). Choose dtm_05m or dsm_05m.
   `https://service.pdok.nl/rws/ahn/wcs/v1_0?service=WCS&version=2.0.1&request=GetCoverage&coverageId=dtm_05m&subset=x(121390,121410)&subset=y(487390,487410)&format=image/tiff`
3. **Large areas as map tiles.** For more than a few hundred metres, download map tiles. PDOK's ATOM feed lists 1,373 tiles of 5 by 6.25 km as Cloud Optimized GeoTIFF; the largest are over 500 MB. Look up the tile number first with the kaartbladindex layer.
   `https://service.pdok.nl/rws/actueel-hoogtebestand-nederland/atom/dtm_05m.xml`
4. **Drop the empty cells.** Cells without a measurement have the value 3.4 × 10³⁸ (the largest float32 number). In our test patch in the Oude Kerk area (Amsterdam) that was 813 of the 1,600 cells. Remove them before calculating averages.

## Interesting combinations
- How tall is every building in the area? → [pdok-bag](https://www.opendataindex.nl/en/bron/pdok-bag.md) via pandgeometrie (RD). For each building from the BAG, take the highest or median DSM value and subtract the surrounding ground level.
- Which neighbourhoods lie lowest? → [pdok-wijkenbuurten](https://www.opendataindex.nl/en/bron/pdok-wijkenbuurten.md) via buurtgrens (RD). Calculate the median ground level per neighbourhood. Use the same projection (EPSG:28992) for boundaries and raster.

## Similar sources
- [3DBAG (TU Delft en 3DGI)](https://3dbag.nl): All buildings in 3D, derived from the BAG and the AHN. Easier if you only need building heights. CC BY 4.0.
- [Copernicus DEM](https://registry.opendata.aws/copernicus-dem/): Global surface model at 30 or 90 metres. Coarse, but consistent across borders.
- [klimaateffectatlas](https://www.opendataindex.nl/en/bron/klimaateffectatlas.md): Uses the AHN to calculate flood depth and waterlogging. Ready-made maps instead of raw elevation.

## What to watch out for
- **PDOK still has AHN4.** The PDOK services contain AHN4, collected from 2020 to 2022 (ATOM feed updated 12 April 2023). The first part of AHN6 (north-east Netherlands, 2025) has been on ahn.nl since 13 October 2025, with its own WMS, WMTS and WCS services.
- **Holes in the terrain model.** Under buildings and on water the DTM has no value. If you need a continuous surface, fill the gaps yourself or use the DSM.
- **Versions are not directly comparable.** Up to AHN4 the DTM was a weighted average, and so was the DSM. Since AHN5 the DTM is an unweighted average and the DSM the highest point; since AHN6 without power lines and pylons. Differences between versions may therefore partly come from the method.
- **Licence differs per version.** AHN4 via PDOK is CC0. For AHN5 and AHN6 the publisher requires attribution (AHN6: CC BY 4.0).
- **Really big.** The whole country at 0.5 metres is 540,000 by 625,000 cells. Work with small extracts or tiles, never the whole country at once.

## API (OGC WMS 1.3.0 + WCS 2.0.1 (PDOK))

- Base: https://service.pdok.nl/rws/ahn
- Access: No key or account needed (tested)
- Formats: GeoTIFF (float32), png, jpeg, json (GetFeatureInfo), COG (download)
- Size: 1373 DTM 0.5 m map tiles (5 × 6.25 km, Cloud Optimized GeoTIFF) in the ATOM feed; the grid is 540,000 × 625,000 cells (tested)
- Filtering: No query language: you pick a layer, a rectangle (bbox or subset) and optionally a pixel.; 

### Endpoints
- `GET /wms/v1_0?service=WMS&request=GetCapabilities`: Layers dtm_05m (terrain), dsm_05m (surface) and kaartbladindex; 9 projections (incl. EPSG:28992, 3857, 4326).
- `GET /wms/v1_0?service=WMS&version=1.3.0&request=GetMap&layers=dtm_05m&styles=&crs=EPSG:28992&bbox=…&width=…&height=…&format=image/png`: Map image (coloured elevation) of a rectangle.
- `GET /wms/v1_0?service=WMS&version=1.3.0&request=GetFeatureInfo&layers=dtm_05m&query_layers=dtm_05m&crs=EPSG:28992&bbox=…&width=200&height=200&i=100&j=100&info_format=application/json`: Elevation at one point in metres relative to NAP (properties.value_list).
- `GET /wcs/v1_0?service=WCS&request=GetCapabilities&version=2.0.1`: Coverages dtm_05m and dsm_05m; formats image/tiff, png, jpeg.
- `GET /wcs/v1_0?service=WCS&version=2.0.1&request=DescribeCoverage&coverageId=dtm_05m`: Extent (RD 10000,306250 to 280000,618750) and grid (540,000 × 625,000 cells of 0.5 m).
- `GET /wcs/v1_0?service=WCS&version=2.0.1&request=GetCoverage&coverageId=dtm_05m&subset=x(…)&subset=y(…)&format=image/tiff`: Raw elevation values as GeoTIFF (float32) for a rectangle in RD.
- `GET https://service.pdok.nl/rws/actueel-hoogtebestand-nederland/atom/dtm_05m.xml`: ATOM feed with 1,373 map tiles (COG) and kaartbladindex.json (1.1 MB); also dsm_05m.xml.

### Parameters
- `layers / coverageId`: dtm_05m = terrain (bare ground), dsm_05m = surface (with buildings and trees); WMS also has kaartbladindex. (tested)
- `crs / bbox`: WMS: crs=EPSG:28992 with bbox=xmin,ymin,xmax,ymax in metres (RD). Also EPSG:3857, 4326, 4258, 25831, 25832, 3034, 3035, CRS:84. (tested)
- `i, j, width, height`: GetFeatureInfo: the pixel within the image whose value you want. 200×200 px over 200×200 m with i=j=100 gives the centre. (tested)
- `info_format`: application/json (GeoJSON with value_list), application/vnd.ogc.gml, text/xml … (tested)
- `subset`: WCS: pass twice, subset=x(121390,121410)&subset=y(487390,487410), in RD metres. (tested)
- `format`: WCS: image/tiff returns float32 values in metres; png and jpeg are images only. (tested)

### Fields in the GetFeatureInfo response (3)
`value_list` String, `geometry.coordinates` Point, `bbox` array

### Limits and pitfalls
- No key and no documented limit. Keep WCS cut-outs small (20 × 20 m = 3.4 KB); for large areas download the map tiles (up to over 500 MB per tile). (tested)
- PDOK has AHN4 (collected 2020–2022, ATOM updated 12 April 2023). Newer versions (AHN5, the first part of AHN6) are only on ahn.nl, via Ellipsis Drive (see components). (tested)
- With a very small bbox (2 × 2 m, 4 × 4 px) GetFeatureInfo returned an empty list; 200 × 200 m at 200 px with i=j=100 works. (experience)
- Cells without a measurement (buildings and water in the DTM) have the value 3.4028235e38 in the GeoTIFF. In 20 × 20 m of central Amsterdam that was 813 of 1,600 cells. Filter them out. (experience)
- There is no WFS and no WMTS at service.pdok.nl/rws/ahn (404). The tile index is a WMS layer and a JSON file in the ATOM feed. (tested)
- The same address also works as service.pdok.nl/rws/actueel-hoogtebestand-nederland/…; the ATOM feed is only under that long name. (experience)

### Example
```
https://service.pdok.nl/rws/ahn/wms/v1_0?service=WMS&version=1.3.0&request=GetFeatureInfo&layers=dtm_05m&query_layers=dtm_05m&styles=&crs=EPSG:28992&bbox=121300,487300,121500,487500&width=200&height=200&i=100&j=100&info_format=application/json
```

## How to fetch it

### curl
```bash
curl "https://service.pdok.nl/rws/ahn/wms/v1_0?service=WMS&version=1.3.0&request=GetFeatureInfo&layers=dtm_05m&query_layers=dtm_05m&styles=&crs=EPSG:28992&bbox=121300,487300,121500,487500&width=200&height=200&i=100&j=100&info_format=application/json"
```

### python
```python
import requests

# Hoogte (m t.o.v. NAP) op een punt in RD-coördinaten, uit het maaiveldmodel van AHN4
x, y = 121400, 487400
r = requests.get("https://service.pdok.nl/rws/ahn/wms/v1_0", params={
    "service": "WMS", "version": "1.3.0", "request": "GetFeatureInfo",
    "layers": "dtm_05m", "query_layers": "dtm_05m", "styles": "", "crs": "EPSG:28992",
    "bbox": f"{x-100},{y-100},{x+100},{y+100}", "width": 200, "height": 200,
    "i": 100, "j": 100, "info_format": "application/json"})
f = r.json()["features"]
print(float(f[0]["properties"]["value_list"]) if f else "geen waarde")
```

## What you can build with it
- [Climate risk check for an address](https://www.opendataindex.nl/en/bouwen/klimaatrisico-adres.md): Type a postcode and house number and get one report on how the building fares on heat, flooding from rain, flooding from rivers and sea, drought and foundation problems, using the Klimaateffectatlas maps, the AHN elevation model, the BAG and real groundwater measurements from the BRO.
- [Solar panel check for your own roof](https://www.opendataindex.nl/en/bouwen/zonnepanelen-check.md): Type a postcode and house number and see how large your roof surfaces are, which way they face, how much sun falls on them and roughly what panels would yield, using open data from BAG, AHN, KNMI and RVO.


## Examples with real figures (1)

For each example the finding, the reference date and the call that fetches exactly these figures.

- **The relief of the hills around Valkenburg, from the Actueel Hoogtebestand Nederland** (AHN4). Table dtm_05m. [Example](https://www.opendataindex.nl/en/voorbeeld/ahn-hoogte-zuid-limburg)
  - `https://service.pdok.nl/rws/ahn/wms/v1_0?service=WMS&version=1.3.0&request=GetMap&layers=dtm_05m&styles=&crs=EPSG:28992&bbox=180000,312000,196000,323000&width=960&height=660&format=image/png`