Making Regional Maps of a World Map

[Lordpassion]

So I have a world map made and I want to start drawing out regional maps. My problem, however, is that I am having trouble getting the shapes and proportions accurate to the larger map. What sort of techniques have worked for anyone else who has made regional maps of their world maps? I was thinking that a grid system may be my best bet.

Note: I hand draw my maps and then do finishing touches in GIMP which I am still learning

My world map

[Vidgange]

Well, first you need to decide what map projection you're using on your world map, I guess. I like using cylindrical projection myself; I've found it a lot easier trying to make a regional map since you can more or less have the latitudes and longitudes as direction markers. If you have a map like this: http://facweb.bhc.edu/academics/scie...atpractice.gif all you need then is a blank paper, draw the long. and lat. accurately (maybe use another map to get those lines right?) on the paper and then use your world map with long and lat as a reference point on where the coast and rivers and everything else should go.

Does any of that make sense?

[Vidgange]

Very cool looking map btw =)

[HBrown]

Well, first you need to decide what map projection you're using on your world map, I guess. I like using cylindrical projection myself; I've found it a lot easier trying to make a regional map since you can more or less have the latitudes and longitudes as direction markers.

I too work from a cylindrical projection. If you use a plate caree projection, you can convert it to any other projection using G.Projector (which is free, btw). I take a subsection of the world map, increase the resolution, and add detail as appropriate. For the final regional map, I convert it to a projection appropriate to the region. For regions with a larger east-west extent than north-south, try a conic projection with two standard parallels. For those with greater north-south extent, a polyconic projection often works well.

The only trick with working with cylindrical projections for a world map is getting the poleward distortion believable. I use G.Projector for this too. Open the map with G.Projector, translate it so the poles are on the equator, and save it. You can make the land look good there, then move it back to the poles in G.Projector again. I usually do this for anything poleward of sixty degrees.

[johnvanvliet]

for areas 90 to 60 North and -60 to -90 south
i would use a polar stereo projection

then convert that to Simple Cylindrical when done

or

if there IS NO LAND !!!!! above 85 n and -85 s

then a correctly mapped Mercator
85 n/s makes a SQUARE map( give or take a bit) 1024 W x 1022 H
89 N/S makes a TALL map 1024 width X 1547 height

[su_liam]

I'm going to assume, to start with, that you have a global map in plate carée projection(or latlong or equirectangular, its all the same). I'll also assume you have a copy of Wilbur. Its down there on my sig links…

In Wilbur, start with a new flat file in a resolution twice as wide as it is high(Width 1024, Height 512). Click Next. Set the Surface Edges to: Top 90, Left -180, Right 180 and Bottom -90. Click Finish.

Now we'll import your texture image. For this example, we'll assume it's in a file named world.png. On the menu bar, open Texture>Shader setup…
Click the Blending tab. Set the box next to Altitude to zero. Next to the Texture box, click Select Texture Image. Select your texture file("world.png"). Make sure that Top is 90, Left is -180, Right is 180 and Bottom is -90. Now you have your worldmap registered to the proper coordinate system.

Now to select your region. For this purpose, I'm going to go with a 20º by 20º region centered at 2ºN/73ºW. Select Surface>Resample>Simple… from the menu. Set your edges to: Top 12, Left -83, Right -63, Bottom -8. Remember: north is the positive vertical coordinate, south is negative, east is the positive horizontal coordinate and west is negative. Top is equal to the center latitude plus half the vertical extent, left is the center longitude minus half the horizontal extent, right is the center longitude plus half the horizontal extent and bottom is equal to the center latitude minus half the vertical extent. To get a square map for our 20º by 20º region to equal values, say 1024 by 1024. I'm not entirely sure Wilbur interpolates the texture properly, but the resulting image can serve as a good guide for accurately drawing your region in a way that is accurate to the global map. If you're as mentally ill as I am, you'll be wanting a worldfile to help you import your map into a gis app later. This should help. If you save your image as region2020_02-073.pdf, then your worldfile will be region2020_02-073.pgw.

Now yer set.

[su_liam]

Hmm. I think I've returned to my old pattern of killing threads. Sorry!

[johnvanvliet]

Hmm. I think I've returned to my old pattern of killing threads. Sorry!

there is no real way around the technical issues of remapping
i would have posted about MMPS ( or ISIS_3 that i normally use) and not Wilbur
but then i use the terminal for a LOT of things

[morikahn]

The original poster hand draws his maps. He wants to blow up and hand draw part of the current map with a high level of accuracy.

I recommend you print a blown up portion of your map and get or borrow a light table. Put your clean paper over the printed blown up portion of your map and trace an outline. With a proper silhouette, you'll be good to go.

[Chick]

Morikahn's suggestion to blow up the area you want to draw is excellent. Then, a window makes a great light table. Tape the map and clean paper to a clear window on a bright day, and you can trace very nicely.