Symbols are used for land features. They're in big chunks so you don't really need a letter to tell you what each space is. For the same reason, houses are left as they were.  

Normal buildings just use the first letter in the site's name. P for Pizza not Parlor. Letters are all lower case and non-inverted. A few places were renamed to cut down on duplicates; power substations are now electric substations, etc.

Multi-tile sites have inverted colors. The road connection or entrance (or lab stair) is marked with a capital letter.

Parking lots part of a multi-tile building are treated as single tile stand-alone buildings. So they have {"sym": 112, "color": "light_blue"}.

Colors mark the (loose) thematic category, with some comprimises between the building's original purpose and its current lootability. 


 
Color = theme. Existing examples. Possible examples.

Light Green= Housing and residential. Houses, apartments, hotels, mansions. Trailer parks, dorms, old folks homes.

Magenta = Retail or supplies. Most misc stores. Any place that sold stuff.

Green = Food, booze, restaurants. Grocery store, bar, restaurant, coffeshop. Brewery, candy shop.

Brown = Farming, nature, outdoors. Gardening Store, cave, campsite, farm, orchard. Hydroponics farm, Mushroom cave, dairy farm.

Red = Guns, military, emergency. Gun stores, police stations, bunkers, FEMA, LMOE, evac shelter. Checkpoints, mil outposts, minefields, army camps. Bandit places?

Light Red = Medical, drugs, cyber. Hospitals, dr offices, pharmacies, vet. Methlab, pot farm, cyber boutique, optometrist, Autodoc. 

Pink = Science, toxins or radition, monsters, weirdness. Slime, fungus, labs, craters. Robot dispatch center, anomalous zones.

White= Tourism, culture, education. Museums, libraries, bookstores, churches, cemeteries.  College campus, theater, gallery. 

Light Cyan = Hardware, tools, construction. Public Works, home improvement, electronics store. Construction sites, machine shops, plumbers. 

Light Blue= Vehicles, repair, fuel. Garages, parking lots, gas stations. Car sales lot, Parking ramps, go cart track.

Gray = Workplaces or abandoned. Offices, mines. Factories, docks, call centers, dumps.

Yellow = Government and public services. Subways, fire, electric stations, sewer plants, banks, prisons. Courthouse, mail center.

Blue = Service and entertainment. (low loot.) Laundromats, gyms, arcade, football field, radio. Movie theaters, amusement parks, spas, hair salons, etc. 
Blue on black is hard to see, so it was used for places you don't often scan the map for. Ponds and related locations that are mostly natural water are also blue with `#` as their sign.