很多时候我们需要计算损失量，比如说河流或者森林，这样我们可以分析其逐年损失的森林面积，具体就是我们需要掩膜空值的区域，然后计算其面积，使用reduce region进行分析。最后我们在制作图表的时候，首先要先建立时间和面积，然后将其集合封装成为一个影像集合，然后分别转化为列表，然后建立一个字典，通过字典的形式将其转化为图表的形式。我们首先要看函数：
reduceRegion(reducer, geometry, scale, crs, crsTransform, bestEffort, maxPixels, tileScale)
Apply a reducer to all the pixels in a specific region.
Either the reducer must have the same number of inputs as the input image has bands, or it must have a single input and will be repeated for each band.
Returns a dictionary of the reducer's outputs.
Arguments:
this:image (Image):
The image to reduce.
reducer (Reducer):
The reducer to apply.
geometry (Geometry, default: null):
The region over which to reduce data. Defaults to the foot