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Lake Region -- gridded population density and county-level administrative boundaries
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This population density grid was extracted from eas-grid.zip and the superimposed county-level administrative boundaries are from e-asia.zip, both produced at the NCGIA and available from the EROS Data Center. The image has been somewhat degrated in comparison with the original in order to produce a .jpg file of appropriate size that will load reasonably quickly over the Internet. The population density levels have been set at the same break points as used on the map on page 16 of the 'Population Atlas of China' (Oxford U. P., 1987), as displayed in the adjacent Key.
This close-up of the Lakes Region displays characteristic freatures of the UNEP/GRID population density grids. The most obvious is that the gridded population densities are not at all homogenous within the administrative units although the population figures from which the grid was generated do pertain to those administrative units. The description of how the gridding was done (http://grid.unep.ch/part2.html) explains that although the total population in each administrative unit is preserved in the gridded data, population densities within them have been adjusted on the basis of 'accessibility' derived from data for road, rail, and water transport, calulated for the nodes in the boundary data (in the first instance, at least).
l. An area roughly equivalent to Poyang Hu (Lake) in Jiangxi Province shows up as white in this image because there are no population data for the pixels, same as for the ocean. This is reasonable as people do not live on the water, at least in this part of China. It would appear that the population of each administrative unit has been distributed only over the pixels that have data, which represent dry land, and therefore correctly represent the overall density of the population per sq km of land area. Most of China's major and some of its minor lakes, as well as portions of the Yangtse River near its mouth, are appropriately represented as 'no data' pixels.
2. However, the region of Dongting Hu (Lake) in Hunan Province has apparently been treated differently, as there are no 'no data' white pixels at all. Therefore, the population of each administrative unit in the region has apparently been distributed over their entire areas, including the surface of the lake, resulting in erroneously low population desities for the dry land in the vicinity of that lake. There are some other similar cases in other parts of China, as well as some hybrid ones, such as around Xin'anjiang Shuiku (Reservoir) in western Zhejiang, where there are fewer 'no data' pixels than there should be to represent the area covered by water.
3. It is a mystery why Dongting Hu was not represented with 'no data' pixels, as some of the relatively small lakes in between the two largest ones were treated in that appropriate manner.
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