What I want to do is to make a curved map grid (longitude and latitude).
Something similar to this grid.
Attachment 50336
Thanks in advance.
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What I want to do is to make a curved map grid (longitude and latitude).
Something similar to this grid.
Attachment 50336
Thanks in advance.
Those lines are called a "Graticule" the particular shape you get depends on the particular projection you use, which depends on the extent of your map (Where it is and how big it is), and the particular properties you are trying to preserve (Angles, distances through a point, areas, etc)
That map is using a Conic projection. I think it's probably Lambert Conformal Conic, although it might be Equidistant Conic.
Grab G.Projector (A free program made by NASA) and load a completely blank image into it. Turn on and configure the graticule, pick and configure a projection, and export the image.
NASA GISS: G.Projector — Global Map Projector
Two other things, remember where you centred the map, and what spacing you chose for the graticule. You'll need this if you want to be able to label the graticule properly. For a conic projection, you want to choose standard parallels close to the top and the bottom of the extent, keeping in mind that they curve.