See more maps by Kaitlin Duck Sherwood, my future plans, and credits.
The darker the red, the higher the value. Median age (which is labeled just "Age" to save space) is on a 25-60 linear scale: any census tract that has a median age under 26 is fully white; any tract with a median age over 60 is full red. Most age ranges are on linear 0-40% scales; under five is 0-15% and 18-21 is on a 0-20% 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.How can I save a map view to look at later?
How can I go to a particular address?
How can I make the response faster?
Why don't I see much color variation in my percentage figures?
Why can't I zoom all the way out?
Why is there a horizontal line sometimes?
Are there census overlays for Google Earth?
Is the author looking for a job?