Relief contour lines in DXF/DWG — terrain for surveyors and civil engineers
Contour lines — isolines of equal elevation — are a staple tool for every land surveyor, road engineer, master planner and landscape architect. On a paper topo map they reveal terrain shape; on a digital underlay in AutoCAD or Civil 3D they are the starting point for siting buildings, aligning roads and computing earthworks. OSM2CDR builds contour lines over any selected area and drops them straight into the DXF/DWG export, together with roads, buildings and hydrography from OpenStreetMap.
Where the relief comes from
OpenStreetMap carries no elevation data — it is a map of features, not of the surface. So we build contours from a separate source: the global Copernicus DEM GLO-30 digital elevation model at a 30-metre grid. This is an open European Space Agency dataset covering all land worldwide, including the high Arctic (the previous SRTM clipped at 60°N — Norilsk, Murmansk, Vorkuta had no relief). For the selected area the service crops a DEM window, runs it through the contour generator, and returns the result as vector lines.
Thin and bold on separate layers
The topographic drafting standard splits contours into two classes: index contours (thicker, elevation-labelled) and intermediate contours (thin). In the OSM2CDR DXF export they land on separate layers, so in AutoCAD you control them independently — line weight, colour, visibility. The interval is set by two parameters: the bold contour interval (e.g. 100 m) and the thin one (e.g. 20 m). The bold must be a multiple of the thin — enforced both in the UI and on the server.
Every line carries an elevation attribute, so elevation labels are bound to real values rather than drawn by hand. When imported into Civil 3D the elevation attribute can build a surface (TIN) — contours become the relief source for design calculations.
Area-adaptive interval
The contour interval cannot be picked blindly: a 10-hectare site warrants a 1–5 m interval, a whole region 50–100 m, otherwise the map turns into solid fill. OSM2CDR picks the interval automatically by selection area when you do not set it manually. A small survey site gets dense isolines, an overview district map gets sparse ones. At very large areas (country or continent scale) contours are switched off — they are physically unreadable there, and generation would eat memory for nothing.
DSM noise in cities
An important caveat for urban sites: Copernicus GLO-30 is a DSM (Digital Surface Model) — a model of the surface with building roofs and tree canopies, not bare ground (DTM). In dense built-up areas contours will stumble over buildings. For a master plan of open land, a quarry, or an out-of-town alignment this is no problem; for a downtown site keep in mind the relief is captured at the upper surface. This is a typical property of open global DEMs and we flag it honestly.
How to get it
- Select an area on the osm2cdr.ru map.
- In the "Topographic features" panel enable "Add contour lines (relief)".
- Optionally set the bold and thin intervals (or leave on auto).
- Choose DXF (or DWG) and run the export.
- Open the file in AutoCAD — contours on layers, with elevation attributes.
Contours work not only in DXF/DWG: they land in all vector formats — SVG, PDF, GeoJSON, Shapefile, KML. For a GIS pipeline take GeoJSON or Shapefile with the elevation attribute, for a print map PDF, for CAD DXF/DWG.