Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Differences between the spatial units used in this study. The size of the spatial unit is listed below the image, and the median size is reported if there are multiple values. The relative sizes of the images are not representative of the actual relative sizes of the units.
