How to Make Your Own:
Donated by Forkboy2
If you want to try to make your own terrain maps, it's pretty easy to do.  You will need a free program called MicroDEM, a good photo editing program that
can adjust brigtness and contrast and also tell you what the color levles are in RGB values.
You will also need some Digital Elevation Model (DEM) data.  For US you can get it free from http://edc.usgs.gov/glis/hyper/guide/1_dgr_demfig/index1m.html
or http://seamless.usgs.gov/ The SRTM data at the second website looks like it might be little bit better but it may have holes so you may just be best off
using the NED data from second website.  I think the NED data is a little better than what's on the first website.
If you are using the second website, you must make sure to download the data in the correct format.  Just zoom into the area you want and select the area to
 download.  Then a window will popup with the download link.  Before you download it, click on button called "Modify Data Request".  Then Select the option
as shown below to download it in TIFF format.
Then click on Save Changes & Return To Summary button to download the data.  When you go to import it with MicroDEM you have to select File|Open Dem
and then select the file type to GeoTIFF.
For outside US, you are probably out of luck until JPL releases the rest of the SRTM data, which given the extra security concerns over 911 probably will never
happen.  You can always do a search for DEM or Digital Elevation Model and your country to see if there is anything for your area.  When looking for DEM
data, anything less than 90 meter spacing probably won't be of much use.  There is some data that covers the whole world with 1km spacing, but it wouldn't
be of much use given the scale.  If you know of some other good sources of DEM data let me know and I'll post it here.
Once you get your DEM data, open up MicroDEM and open the DEM file.  Most of the formats can be opened just by going to File/Open DEM.  Some formats
need to be imported first which you can do by clicking on In/Out button to bring up Data Manipulation screen and then click on import which should give you
something like this:
Next right click on the image somewhere and select "Display Parameter" from the menu that pops up.  Then another menu will pop up, select Elevation which
will give you something that looks like:
However, we want it to be greyscale, not color so right click on it again and select Elevation Colors which will make another menu pop up an select Colors.
Then select Gray Scale.  You can also check Ocean Check which will have MicroDEM try to determine if you have any ocean and it will color that blue.  This
comes in handy later.  Lake Check usually doesn't work so don't check that.
Once you do this your DEM should now look like:
Next use the buttons at the top of this screen to select the specific region you want to import into SC4.  The 4th button from left lets you zoom into a box and
the magnifying glasses let you zoom in and out.  You will need to compare the DEM to a street map or something to figure out where exactly your city is
located and the scale.  You want it to be a scale of about 10-12 miles on each side if you want it to match up with SC4 scale.  Of course if you are just trying
to make a cool terrain and not worried about the scale, this doesn't matter.  In the image above, the blackest area is a river or valley and the white area is a
mountain peak.  Also, zoom in a couple extra times to make sure the image you export is greater than 1025x1025 in size.  Usually if you zoom in 4x that will
do it.
Another little trick you can do is to right click on the image, select Colors and then select Specify.  This allows you to change the color range of the DEM.
This might be useful if the DEM imports into SC4 and the mountains are too high or not high enough.  Basically if you want the mountains to be low make it
darker, if you want them to be higher make it lighter.
To export it, you can either go to file menu and select Save Map as GEOTIFF or you can just right click on the DEM and select Edit if you have your photo
program set up as default editor.
Next use your photo editing software (I'm assuming you have Photoshop, otherwise instructions may differ a little) and first resize the image so it is exactly
1025x1025 pixels.  You will also have to crop off the scale bar at the bottom, which imports from MicroDEM.
Next, make sure the image is in RGB mode and use the color picker to move around the image and notice that the RGB values change from 0 to 255.  Try to
find the lowest (blackest) and highest (whitest) points on the image and make a note of those values.  Also determine where you want water to be.  Most likely
the water will be the darkest area.
If you don't have any water at all  then you don't need to do anything further adjusting of brightness or contrast.  If you do have water you need to figure out at
what level the water is at in the DEM and then subtract that number from 85 and increase brightness by that amount.  For example if water is at brightness
level of 10 you would want to increase brightness by about 74 or 75.  Then What I do is fill the water elevation with a color that is about 75.  This makes it so
the water is deep enough.
If you have mountains in the area you can also adjust the contrast to make sure the highest point is level of 255.  You will need to play around a little with
brightness and contrast to get it just right, but this should get you started.  Also, you can add rivers and streams by painting lines with level of 75-80.
Also, if you had MicroDEM make the Ocean blue, then you can fill those areas with grey scale brightness level of less than 85 to turn those areas into water.
Once you are done changing the image, convert it to a 8 bit greyscale and save it as BMP or JPG.  That's it!
Here is a catalog of international DEM data.  It's kind of old but may be of some use to people trying to make their own.
If you are having problems understanding how to adjust brightness and contrast when making your own here is some more explanation on how I adjust
brightness and contrast.
What I do is first look to see what level the water is at. For example lets say the water is at brightness of 10 and the lowest land area is at 11. Next I set the
background to a brightness of 1. Then I will use Photoshop to select all pixels with brightness of 10 and cut them out which leaves water areas with brightness
of 1. Then I go thru an manually fill in some areas with brightness of 1 if I want to add some more rivers or something.
At that point I have a pretty good difference between water and land which will make sure the water is a little deeper than just 1. Then I increase the brightness
of the whole image to make the lowest land be level of 86. So in this case I would increase brightness by 75 since the lowest land are was originally 11. This
leaves the lowest land area at 86 and the water would at 76.
The other thing to watch out for is to make sure when you increase brightness it doesn't leave all your mountain tops flat. If you have a lot of areas with a high
brightness of over level of 200 and you increase the brightness by 75 it will flatten out the tops of your mountains because large areas will end up with level of
255. If you have this problem you first want to make sure and adjust the contrast so you mountain peaks are a little darker before you increase the brightness.
Also, if you are just going by the greyscale percentage instead of RGB values to determine water level, the water level should be right around 66 or 67%.
(1-85/255)
Some Limitations:
Can't have water at different elevations.
Really big mountains may not look as high as they are in reality.  If we could figure out a way to get water level down to 20 or 30 instead of 85, we could fix
some of this problem.
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