Geoscatter point size in km

Hello,

I am trying to show some point on a geoscatter plot, but I am not able to set the right size.

Let's say I want to plot a 500km*500km circle on the equator line, coordinates 0,0 , how can I apply the size? (on the equator, otherwise it should be bigger depending on the latitude).

This is what I found in the documentation: "Specify the values in point units, where one point equals 1/72 inch. To specify a marker that has an area of one square inch, use a value of 72^2."

I found that 1 cm is around 28 point units, so I tried to set a size of pi*(250km*28.346^2) (it is a circle, so the area is pi*r^2), but the scale depends from the zoom level and the size of the chart.

Moreover I think it should not be a circle, unless it is plotted on the equator line, but a ellipse because of the proportions, how can I plot it?

Thank you

[darova]

Can't you manually draw an ellipse?

Answer 1

[dpb]

I don't have the mapping TB so can't experiment, but looks like <geobubble> would be better suited to the purpose as it does have a scaled to an input data array size argument. It doesn't appear to have the sophistication to do more than draw a circle on the map at the location, however; no projection onto the surface.

[Iacopo Torre]

Thank you for your suggestion, I had a look at geobubble, it's really nice, although it still does not allow me to choose a real scale in cm/km, so some bubbles are bigger, some smallers, but they do not respect the scale.

[dpb]

I think you can make do so by judicious selection of the various parameters. But, plot uses points as diameter for marker while scatter is scaled to area so you can compute the needed size values.

Not having the TB I can't experiment directly but there are a couple other parameters that work with the size array to set the actual drawn diameter.