Tiling and mirroring are useful for creating patterns based on a simple image. Use them when you need wallpaper and other repetitive designs.
Left: A bitmap
Middle: Tiling the bitmap
Right: Tiling and mirroring the bitmap
The Tile option in the Material Editor is on by default, repeating the image along the U and V directions. You can use the Tiling values to scale the map image. Setting negative Tiling values increases the size of the image.
You can also set tiling values in the UVW Map modifier. These settings are in addition to the tiling values you set for the map in the Material Editor. If the map's base tiling parameter has a value of 2.0 and the UVW Map modifier has a tiling value of 3.0 for the same axis, the net result is 2.0 x 3.0 = 6.0. To avoid confusion about where the tiling is coming from, you may want to set the map's tiling in its base parameters or with the UVW Map modifier, but not in both locations.
The Mirror option is a variation on the Tile option. Tile repeats the image side-by-side, while Mirror flips the image repeatedly.