Mathematica Asked by K7PEH on July 28, 2020
I am using PlotRange to clip a GeoGraphics plot so that I can center an area of interest. However, I do this via trial-and-error because I have no idea how PlotRange coordinates specified as PlotRange->{{-0.4,.6},{-.25,.4}}
which properly clips the geographic result.
But, what am I doing? In an ordinary coordinate plotted graph I am controlling the range of the coordinate axis over the plotted range of values. But in a GeoGraphics plot it seems that the maximum range of these coordinates is plus and minus 1 for each axis (horizontal and vertical).
This a guess because there is no documentation under PlotRange that describes how it is being used with a GeoGraphics plot. And, under GeoGraphics documentation, there is no explicit mention of PlotRange.
Question: what is the meaning of the numeric values specified in PlotRange coordinate limits. Are they fractions of a whole projection and if so do they measure anything (certainly not longitude and latitude lines that I can tell).
As @BobHanlon mentioned, you actually want to use GeoRange
rather than PlotRange
for GeoGraphics
as this is what the documentation suggests. Also, you might want to use GeoCenter
to centre your GeoGraphics
(and using GeoRangePadding
to add to your view range, or GeoRangePadding -> None
to set the default padding off), rather than moving PlotRange
or GeoRange
about.
One of the more useful things about using the Geo*
functions is that most of them work correctly with geographic entities, so you can also do GeoRange -> Entity["Country", "UnitedStates"]
which is often more useful than setting it to specific lat/lon ranges.
Anyway, if the projection is equirectangular, GeoRange
and PlotRange
do almost same thing for GeoGraphics
, but the X and Y is reversed - it is {{-lon, +lon}, {-lat, +lat}}
for PlotRange
and {{-lat, +lat}, {-lon, +lon}}
for GeoRange. In both cases lat
and lon
are absolute angular degrees by default.
However, if the projection for your GeoGraphics
is not equirectangular, PlotRange
will use the native units for your projection, which is nearly always confusing and not what you want. This is a big reason to use GeoRange
instead of GeoGraphics
, especially as GeoGraphics
will automatically change projections based on the size of the range by default.
GeoGraphics[PlotRange -> {{-10, -6}, {53, 56}},
GeoGridLines -> Quantity[.1, "AngularDegrees"], GeoProjection -> "Equirectangular"]
GeoGraphics[GeoRange -> {{53, 56}, {-10, -6}},
GeoGridLines -> Quantity[.1, "AngularDegrees"]]
Correct answer by Carl Lange on July 28, 2020
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