I did these maps for the original retail game, piecing together screenshots. The GOG version has different area map numbers but they areas did not change.They show where each sewer opening is in the city. If you have a small monitor, a viewer with a zoom feature like Faststone is helpful.

These are pretty neat; the BG city map reminds me of an online one. Thanks for sharing.

One note: the area numbers (you mentioned the GOG number changed) will be different if you play in TuTu or BGT. The original BG1 (GOG) has the correct numbers. For example, if you press CTRL+X ingame in the sewers where you meet the Ogre Mage, you will get AR0226, the correct area.