LoL! Well.. best thing for it, in my opinion is 'TXD Workshop'. Google for it and download it. I don't wanna share links.
Simple tool, just run it, open gta3.img (in gta:sa folder-models). There you will see all the txd's and dff's. Note that txd's will have a picture preview of each file contained.
Not sure how is the map thing or radar thing called but just search for it. Then, when you find some specific file (txd) you want to edit, just click on the texture and left click- extract file as (png, bmp...). Then open extracted file with paint dot net and edit it the way you want.
btw. You could google for "detailed radar mod", for san andreas, so it can help you find files and replace and edit them.
So in short: TXD Workshop - play with .img's - Paint Dot Net - edit - import edited png's back to txd file (remember to keep the same names) Click save - done.
Test game with every few things you edited, so your SA wont crash.
WARNING: Do not replace PNG files with TXD files, as PNG's is what TXD is made of (some have multiple images)
REMEMBAR TO DO BACKUP!
