I've been learning how to use Cartopy and Matplotlib to plot map. But I have a question regarding the argument transform. According to the Cartopy document, transform specifies "what coordinate system your data are defined in". Suppose I am going to plot temperatures of an area, and the area has been split into several grid cells. Each grid cells has a corresponding coordinate defined in lat and lon (Geodetic Systems). Based on the Cartopy document, I need to use crs.PlateCarree() instead of crs.Geodetic(). I'm a bit confused about it. Because,I think the PlateCarree is a way of projection. In other words, coordinates defined in PlateCarree projections are projected data. But latitude and longitude should be unprojected data. Can anyone help me with it? Thanks!
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1If the plot involves lines, `transform=crs.PlateCarree()` transforms/draws straight lines along supplied data points, the results can be bad if distances between points are long. Instead, `transform=crs.Geodetic()` will add extra points along the supplied vertices to obtain the plots of long lines as greatcircle arcs that make the plots more accurate. – swatchai Jun 20 '22 at 22:14
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1Clearly, `transform=crs.Geodetic()` will do much more computations than the other. If you don't need greatcircle arcs in your plots, you should use `transform=crs.PlateCarree()`. Both provide similar coordinates transformation in the process. – swatchai Jun 20 '22 at 22:26