25G for any file that needs to be called into a program is too much. That file needs to be optimized whether is with different versions of the data, such as a text files with the information, a svg, png, bitmaps with the xml description, different layers of the highways, etc.

The large image could be split into smaller sections capable of taking a single screen of made to form panoramas. I don't know; there are many ways to optimize files by changing formats, organizing small chunks and calling them through a smaller java-script program or library.