Step One : Name your map and decide the dimensions.
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Step Two + Three : Now select the grass floor, and the flood tool.
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Step Four : Fill the floor with your grass tile
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Step Five + Six : Grab your double trees and select the pencil tool
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Step Seven : Now this is where it gets fun. As you know, nature is random, so do a sketchy outline of how you want your map to look. Mine is as follows.
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Step Eight : No, don't do anything else yet, you're not done yet, do it again, but fill in the outsides like this
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Step Nine : Now that you have a basic outline, add some random details. Don't be afraid to express yourself.
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Step Ten : Now, lets finish up the map by adding some finishing touches (the tree tops and bottoms).
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This may have not been my best map, but it gets the point across. Using this technique, you can be a pro
at mapping nature. With a little imagination, you can add/delete stuff, make pathways, waterfalls, or whatever. ^.^