Bumping doesn't remove every object from the map. A seemingly random selection of objects are removed. In reality, the same objects are removed each time. Tall Gray Security Doors (TGSDs) disappear often, but certainly not always. The only way to know which objects will bump out of a given district is to bump it. Of course, you also have to know which objects are normally supposed to be there! I did the whole laborious before-after catalog of each door in a district some time ago in order to produce
this map of D06. You don't see it (because I hid the layers) but I cataloged every single door in the district first. I bumped it and then revisited every door to see if it had been bumped out. Finally, I noted the ones which bumped out and made the map.
Obviously this could (and should, IMHO) be done for each district. It takes time, though. I have been trying to focus my ODST efforts with the SGP recently (*cough* Weekly Challenge *cough*) but this manner of cataloging will likely resume (on my part, anyhow) once other areas of investigation have settled down.
