I work for a social services agency, and my guesstimate is that 70% of the managers think that zip codes are the answer to all their spatial analysis problems -

I work for a social services agency, and my guesstimate is that 70% of the managers think that zip codes are the answer to all their spatial analysis problems -- they are very easy to collect, and they feel right. These managers don't really have any training in geography, so it isn't exactly surprising, but I think there is a pretty strong committment to zip codes as the unit of analysis because it is the one thing they know and think they understand. For the folks who in this thread say "just use a point map of occurrences and you would have seen the problem" you are right in this case, but it isn't really enough in most cases. For one, the boundary of the city limit needs to be shown to see the correlation; perhaps one should map the point occurrences a la Snow, and then overlay all the boundaries you have (mosquito district, city boundary, water district boundary, county, etc...). Additionally, a point map doesn't tell you rates of occurence, for that you need a denominator, or you can't calculate things like number of occurences divided by total population. One poster mentioned Census Tracts, and I would agree those should be the default boundary, subject to more investigation -- tracts correpsond well to "natural" boundaries, they are mostly consistent over census decades, they are mostly consistent with population (~5k), they nest perfectly with other census boundaries, and they are the smallest geography for which you can get mostly the full suite of population characteristics like education from the ACS. For some reason tracts feel just wrong to people. I have managers who reject zip codes, but then fixate on weird systems like pixels or equal area hexagons or whatever for which you can't get denominator data and which don't correspond to anything real. I don't understand, though I don't think in public policy / social work education anybody bothers to teach you shit about GIS or Census data unless you know to ask specifically.