How do i make buildings symmetrical?

I have been editing for a while now and i was wondering how to make buildings symmetrical.


There’s no perfect way. A few suggestions:

  • Make use of the “Q” key in editors to make building corners square.

  • Draw half the building, duplicate it and then reflect the duplicate. Carefully position so that nodes can be joined. In iD (the default online editor) it is a bit complicated to merge these, but there is a trick. As long as iD doesn’t know that an object is a building you can cut it (if it is a building cuts will create a relation) so that you can remove the duplicated segment and then using “C” merge the two halves. I add an “x” to the building key and remove it afterwards.

  • Make use of untagged lines to guide your edits. These can be automatically straightened. Nodes can be spaced at regular intervals, etc.

  • Measurement tools are available in iD, Josm and Vespucci. They can help ensure that protruding parts of buildings are the same width & length if guide lines can’t be used.

  • Josm provides the best support for building mapping (merging polygons, angle snapping, extrusion, etc.). I often use it to improve the outlines of buildings I have already mapped in another editor.

  • The wiki has some quite detailed advice about drawing complicated buildings (although not symmetry).