The cities that stretch across the U.S.-Mexico border are studies in contrasts. Maps portraying the areas show dramatic differences defined by the dividing line between the nations in educational levels, employment, and other variables. The San Diego-Tijuana Interactive Atlas shows the difference a border line can make for two particular cities at many levels.
The site is laid out very simply and is easy to use. A pull-down menu lets visitors select variables like "population 18 to 35," "population with eight years of school," or "renter occupied units." Users can choose whether to show freeways and city names on the map, and can select whether the map will be broken into quintiles or equal intervals.
The map produced showing the percent of the population aged 5 and younger shows that practically all of Tijuana consists of areas where 15 percent or more of the people fall into this age group. North of the border, the percentage drops off fairly dramatically, with several census tracts where the share is 6 percent or less.
When the setting is changed to the percentage of housing units with running water, the map flips. Practically all the census tracts in San Diego have water in 98 percent or more of houses. In Tijuana, only one area falls into that category, and a large share have running water in 62 percent or less of homes.