None of the buildings are taken from Google Earth, though it may be used for measurements and asset placement in the game. They may also visit the the locations featured to take photographs and measurements, as well as using technical drawings and plans. Many of the assets are created in-house by DTG's art team, however other companies such as Skyhook Games are also contracted to produce content, both for TSW and TSxx. They may also purchase the rights to use assets from third party DLC. Some of the rights to assets created in projects I have previously worked on are now owned by DTG, and they still use them in TSxx DLC.