You have to locate and remove the cells listed below then the map should be visable. If its a new play through then just install and play like normal.

I have not used the following link but supposedly it works to make it simple (I do NOT know NOR ever used it before so no idea how it works, Found it with a simple google search)

https://grabofus.github.io/zomboid-chunk-cleaner/

The map takes up cells:

24,44 25,44 26,44 27,44 28,44 29,44 30,44 31,44 32,44 33,44 34,44 35,44 - road
connection
13,45 13,46, 13,47
14,45 14,46, 14,47
15,45 15,46 15,47
16,45 16,46 16,47
17,45 17,46 17,47
18,45 18,45
19,45 19,46
20,45 20,46 20,47 20,48
21,45 21,46 21,47 21,48 21,48 21,49 21,50 21,51
22,45 22,46 22,47 22,48 22,48 22,49 22,50 22,51
23,45 23,46 23,47 23,48 23,48 23,49 23,50 23,51
24,45 24,46 24,47 24,48 24,48 24,49 24,50 24,51 - The town it self.