SimCity 4
SimCity 3000 Compatibility
UTILITIES
All but the Hydroelectric plant made it over to SimCity 3000 from SimCity 2000, giving it a total of eight varieties of power plant (Coal, Oil, Gas, Nuclear, Wind, Microwave, Solar, Wind, and Fusion), all of which were 4x4 buildings, except for Wind, which was 1x1. In SimCity 4, it's a little different. Coal, Oil, Gas, and Nuclear continue to make over unscathed, but the Wind Mill is now a 2x1 building, the Solar Power Plant is now a 6x6 building, and the Microwave and Fusion power plants aren't there (instead, there's the Hydrogen Power Plant, which is a 6x6 building). As far as water buildings go, water towers are now 1x1 (instead of 2x2) and the Desalinization Plant is gone. The Incinerator is also gone.
TRANSPORTATION
Roads still are going to be fine if transferring over (highways maybe, they have more finicky placement, though they could be replaced with Avenues in a pinch). The main issue is Railroads. The first thing is that they're not compatible with Subways anymore, so that the subway-to-rail systems would be cut off from each other, and Railroads cannot make 90° turns anymore (I'm not sure about subways doing the same thing). Subway stations are fine, but the replacement Train Station would have to be the Passenger Train Station, which is a 2x3 building. Additionally, Bus Depots (4x4 buildings) are replaced with the more compact 1x1 "Bus Stop". For a game that pushes transit, you will have an easier time bringing over roads.
PUBLIC SAFETY
The old Fire Stations were 3x3 buildings, whereas SimCity 4 has the Small Fire Station (1x2) and the Large Fire Station (3x2). The Large Police Station (3x3) is compatible with the older Police Stations, though!
HEALTH & EDUCATION
Hospitals (3x3) have no direct replacement, there's only the Large Medical Center (4x3) and the Medical Clinic (1x2). Likewise, Schools (3x3) were split into Elementary School (2x3) and High School (4x4). There is the 3x3 Major Art Museum but the closest to the 3x3 Museum, the City Museum fits the bill, which is 2x3. The 3x3 City College got replaced with a 5x3 building. Only the Library (2x2) is compatible with the Local Branch Library (2x2). Basically, you would need to do a complete overhaul of the health and education system as well.
PARKS
The Small Park and Fountain (1x1) has a variety of 1x1 buildings (Open Grass Area, Open Paved Area, Small Flower Garden, among others) to replace it. The 3x3 Large Park has Large Park Green which is also 3x3. There are other 2x2 buildings (Medium Park Green and Medium Playground) to replace SimCity 3000's 2x2 park structures (Pond, Playground). The Marina is a reward (and is a 1x6 building, nothing like the 3x3 building), as is the Zoo (now 8x8, and also a reward). The Sports Park (4x4) has no equivalent.
REWARDS
Courthouse (3x3) and Statue (1x1) look to be the only ones that are compatible. Everything else isn't.
LANDMARKS
A lot of the landmarks already got replaced between SimCity 3000 and SimCity 4, I would assume none of them are a match.
Like the differences between SimCity 2000 and SimCity 3000, a conversion would leave quite a mess on your city. At least zones are fine for now (though Light Industrial would become Agricultural).newcity/newcity.html">some great ideas, and the less said about Cities: Skylines II the better. But perhaps AI could help. Already, as of this writing, a third of SimCity 4's code has been decompiled (this stemmed from a previous attempt at making an open-source SimCity 4...which was basically a SimCity 4-compatible knockoff) and that could lead to patches that address core problems (like crime affecting larger lots) rather than just DLLs that attempt to address it, as well as fixing a lot of the hard-coded issues. Maybe we could even create a way to bring SimCity 3000 buildings to the game as intended...and AI could also make buildings, too, I suppose...years ago I remember releasing a list of buildings I "planned" to make, armed with a handful of Microsoft Bing Birds Eye View pictures and other "sources". Over at the Carbon-izer.com Archive there's a 50MB(!) aerial of Northwest Plaza, a mall in the Saint Louis area I was interested in at the time. (After all, SimCity 4 is missing nice regional malls...among other things). It's missing other angles (I may have saved other angles), but I think technology already exists to make that into a 3D building. Maybe SimCity 4 was the city sim that was what we really needed after all. Maybe.