Welcome to the wonderfull world of height maps. What can i say, these can greatly help you when creating a new map. Instead of spending hours raising and lowering your map just create one of these beauties. There is very little you will need to know of do. All you really need is a decent Paint program or demo. Pain shop pro is what i recommend to start with, plus its cheaper if you want to buy a full copy.
To start your height map first open the graphics program. Once you have it open create a new file. This file will need to be the exact map size up to 250x250. One thing you must have set, is that this file will be using greyscale color. A note of the greyscale, white is the highest level on the map while black will be for the lowest points. Once you have the pic done how you like, save it.
When finished, open Edit world. Create a new project the same size as your pic. Once you have that done and the dataset loaded import the pcx file into edit world. Thats all there is to it. See how much time you saved?