The darker the red, the higher the value. Average household size has a linear 1 to 5 scale: Census tracts with an average household size of 1 show up as full white and anything over 5 shows as full red. All other demographics are on a linear 0-50% scale.I don't draw borders on the tracts that only take up a few pixels. That's why urban regions tend to have a ring around them with no borders. NOTE: when you are looking at census data, the farthest you can zoom out is to see roughly 2/3 of the US at once. (At some point, I'll make the tiles for farther-zoomed out, but not right away.) In the other direction, Google added a few more zoom levels in API v.2 that my tile server doesn't know about. It usually isn't interesting to zoom in that far, so fixing that isn't a priority for me. You will have a better experience if you clear your browser's cache before doing much.