In the previous chapter we created a simple map built of two tiles.
Any game developer must have laughed a lot - two tiles are a really
poor tileset. You can look at tilesets shipped with freeVikings -
you can find them in directory gfx/tilesets/.
Since all of them are really poor, you'll probably want to make your
own.
Most of levels from the default campaign (ice levels etc.) are
legacy from "pre-Tiled" epoch. They are built of tiles stored
file-per-tile; you can find them in subdirectories of
gfx/themes/ (together with images
of some theme-specific objects).
Tileset is simply a PNG image where tiles are painted next to each other without any gaps. All tiles of a tileset must be of the same size. Recommended tile size is 40x40px. However, freeVikings releases after 0.6 support even custom-sized tilesets. The only limitation is that all tilesets used in one map have the same size (even if Tiled provides limited possibility to combine different tile sizes in one map!)
It is really important that your tileset image is in PNG format, because Tiled can't work with other graphic formats (freeVikings can).