I use prefixes on some of my tags. Here is a short primer:

state: The name of the largest political entity below country (state, province &c.) in which the photo was taken.

Example: state:washington

loc: The census-designated place (city, town, village &c.) in which the photo was taken. city: was not used because not all census-designated places are cities.

Example: loc:tacoma

nb: The neighborhood or district in which the photo was taken.

Example: nb:stadium district

street: The photo is of the named street or the photo was taken on the named street but does not necessarily include the roadway.

Example: street:stadium way

addr: A short description of the place (not the actual address for privacy reasons) the photo was taken. Only places that do not otherwise have a name are assigned names using this tag prefix.

Example: addr:apartment [ap:]

geo: The latitude and longitude of the location where the photo was taken. Only used when a specific location is difficult to specify using the previous location tags.

Example: geo:47.263374 -122.445549

sign: A summary of text in the photo.

Example: sign:detour

project: A summary of the construction project which is the subject of the photo. This is a new tag prefix, and the "construction" restriction may be removed in the future as usage is expanded.

Example: project:stadium way

camera: An identifier for the camera with which the photo was taken, whether my own or the property of others. This is often, but not always, the same as the photographer. Photos without this tag can be assumed, unless specified, to be from my main camera.

Example: camera:ben

xx: Some tags include at their end a two-letter designation in square brackets. In the earlier addr: example (addr:apartment [ap:]), [ap:] is what I'm taking about. This is the tag prefix to be used in relation to the parent tag. Accordingly, ap:kitchen would be used for photos taken in the kitchen of my apartment. Photos taken in or of the garage at addr:dad's house [dh:] would be tagged dh:garage.

I am not a lawyer. This is not legal advice. This does not create an attorney-client relationship.