This graphic illustrates how the US Census organizes their data. The smallest unit is the "block". It usually corresponds to a city block, but in rural areas where population density is low, it can sometimes cover a mile or two.

Information at every level is available free from their website. I have been working mostly with data at the county and the block group level. Great stuff for further analysis of just about any map.

For example, I could download home values and overlay that on top of a map of the California fires, and very quickly come up with an estimate of the cost of damage. Pretty exciting stuff!