Gymnasiast created a 233x233 map which amounts to a larger size than the base Zoo Tycoon 1 game allows. The base game has a maximum map size of 150x150.

From Gymnasiast:

The map size is saved using a 32-bit integer, which has a theoretical maximum of about 2.1 billion (or 4.2 billion in certain circumstances). In practice though, testing with different map sizes has shown that 233×233 is the maximum that ZT1 will load. Anything bigger and it will freeze while attempting to load.

But then, having a 233×233 map is still quite an improvement from 150×150, is it not?

To install, unzip the file and drop the .zoo within inside of this directory: C:\Program Files\Microsoft Games\Zoo Tycoon\Saved Games

You can find Gymnasiast and his other work on Github: https://github.com/gymnasiast