A heightmap is a grayscale image that represents the elevation or height of a terrain surface. Blender provides built-in support for importing heightmaps as a way to create a 3D map. Here are the steps to use a heightmap in Blender:

1. Create a 3D Map of the desired area and download the Texture and Heightmap set. If you need you can use the 16 bit option in the exporter.
2. Import the heightmap image: In Blender, select “File” -> “Import” -> “Images as Planes” from the menu, locate the heightmap image, and select it. Blender will import the image as a plane object.
3. Add a displacement modifier to the plane: In the “Modifier Properties” window, select the “Add Modifier” button and choose “Displace”. In the “Texture” section of the modifier, select the imported heightmap image as the texture. Adjust the “Strength” value to control the height of the terrain.
4. Convert the plane to a mesh: Select the plane object, and then select “Object” -> “Convert to” -> “Mesh from Curve/Meta/Surf/Text”. This will convert the plane object to a mesh object.
5. Adjust the mesh settings: In the “Properties” window, select the “Object Data Properties” tab and adjust various settings for the mesh, such as the number of subdivisions or smoothing.
6. Add texture image: In the “Shader Editor” window, add texture image to the mesh to give it a more realistic appearance.
7. Save and use the 3D map: Once you’re happy with the 3D map, save the scene and use it in your project or export it as an OBJ or STL file if you need to use it in other software.

That’s it! Using a heightmap can be a quick and easy way to create a 3D map in Blender.