From The TimeSplitters Wiki

Tilesets are Mapmaker tools used for adding the feel of the map. Each game has a few tilesets. Changing the Tileset can greatly affect the feel of the level, for example, in TimeSplitters 2 an Industrial Tile map would look like an old, abandoned factory, while changing it to the Alien Tile would give a clean, space look. Additionally, each tile set has 1 or 2 rooms that completely change their looks depending on the set. The various tilesets found in each game are described below.

TimeSplitters

Alien: A stone shaped area with holograms and ramps.

Spaceport: A futuristic airport with seats and spaceships, very similar to the Spaceways map.

Industrial: A weapons base with air vents and a missile silo. It is based off of the level Cyberden.

Gothic: A medieval style church Tileset. The large room tile features stain glass windows which can be smashed.

Virtual: A silver style map that has no objects.

TimeSplitters 2

Alien: A clean, bright tileset with laser doors. The only colours are white and orange.

Victorian: This map is based off of the architectural style of the late 19th and early 20th century. Many consider it to be the most popular Tileset in TS2. Due to its versatility, it can be used to create many differently themed maps, such as houses, factories and haunted mansions.

Virtual: The TS2 Virtual Tileset is similar in style to the Tileset of the same name in TS1, but unlike the TS1 version, it has a blueish hue.

Industrial: A dank, dirty Tileset. It is most likely to be used in sewer and abandoned factory maps.

TimeSplitters: Future Perfect

Military: An army bunker Tileset that has mine pits and acidic pit tiles. Default Vehicle: Jeep

Lab: This Tileset has silver metallic walls and is generally sci-fi in appearance. Default Vehicle: Buggy

Horror: This map is somewhat similar to the Victorian Tileset, but the appearance of the Tileset has been modified for use in haunted mansion Tileset ala Mansion Of Madness almost exclusively. Because of this, the Tileset's usability is somewhat limited. Default Vehicle: Jeep

Egyptian: As the name implies, this Tileset makes great use of Egyptian hieroglyphics and paintings on the walls. The map's walls are a reddish-brown, as though they are sand-worn. This map also shares a strong resemblance to the TS1 map, Tomb. Default Vehicle: Jeep

Virtual: This Tileset remains relatively unchanged from its predecessors, though more attention has been cast to detail. Default Vehicle: Modified Buggy