Area map is a two-dimensional grid of characters, where each character describes the geographical makeup of the space it's occupying or, alternatively, designates the current position of a living organism.
Specifically, the space character ( ) represents open space, the tilde character (~) represents water, and the hash character (#) represents an obstacle. Living organisms (plants and animals) are referenced using their corresponding one-letter identifiers as defined in the list of species.
Here's an example of a 49x13 area map (source) that corresponds to this list of species:
~~~ ### aaaaa
~~ D B B ### C aaa
~~ aa aaa B ### aa a
~~~ aaa aaa ### D aaa
~~~~~~ aaa aaa ### A
~~~~~~~~ aaa ### ~~ A
~~~~~~~~~ A ### ~~~~~~
~~~~~~~~~ A ### ~~~~~~~
~~~~~~~~ B C ~~~~~~
~~~~~~~ bbbb bb ~~~~~~
~~~~~ C aaaa bb bb bb ~~~
~~~~ C aaa aa D b ~
~~~ aaa aaa bbbbbb bb C