An Indexing Problem

The picture above, from the HABS survey of downtown Providence, Rhode Island, is a litmus test. Is the first thing that you thought of when you looked at it “trash can”? Was that the tenth thing you thought of? I have a small amount of familiarity with downtown Providence, but that’s not why I looked at this survey. I looked at it because I couldn’t imagine why “trash cans” was in the index to HABS surveys. This is the only survey with that keyword. There are eleven photos and I found two with trash cans reasonably visible. Here’s the second:

These are both photos of active cityscapes with buildings and street furniture of varying ages, but personally I find the trash cans to be uninteresting. 

The problem with an index is that if doesn’t have enough items then people can’t find what they’re looking for; if it has too many then it’s unwieldy. This survey has 47 keywords, some of which – “bus” for example – seem overly obvious and somewhat unrelated to the point of the photos. This survey is about the more-or-less permanent buildings of the city, not the busses that may be seen on the street. And I’ve now devoted 219 words more to the probably-mistaken inclusion of the two words “trash cans,” demonstrating how signal-to-noise ratios degrade.