GDP per capita has little meaning when the area is divided into specific areas. I.e, if you put a guy in a desert with an oil field, the GDP per capita is huge. If you have a very productive place that is productive because of the high population, you have a low GDP per capita.
People go where the money is. The more people arrive, the lower the GDP per capita sinks. In the end, the only places with high GDP per capita are mines and oil fields, etc.
The map is meant to show relative GDP per capita. Tokyo is very dense, and has an extreme GDP per capita compared to most other comparatively dense cities in China. Your man in an oil field is not part of this exercise, except where of course, he is. But if you know your intra-China geography, the "oil fields" are pretty obvious.
Some of the anomalies of the map suggest overreliance on official figures that don't capture all the genuine economic differences among those various regions. The map is interesting in showing huge regional disparities among regions of China ruled by the P.R.C. regime. That issue of regional economic disparity is worrisome to social scientists in the P.R.C., as economic disparity among regions of the country is believed to be one reason for the disintegration of Yugoslavia.
People go where the money is. The more people arrive, the lower the GDP per capita sinks. In the end, the only places with high GDP per capita are mines and oil fields, etc.