Tileset creation guide
Tilesets are images used to create backgrounds for levels in 2D video games. We use tilesets to design all the levels in Journey to the Center of Hawkthorne.
Individual tiles are 24 x 24 pixels. They can overlap each other; however, they can't be offset. Tiles must be placed at intervals of 24 pixels. Tiles can be rotated by 90 degrees as well as flipped over both the X and Y axis. Take a look at the Town level to get an idea of how this plays out:
The above image is not a tileset. A tileset consists of the unique tiles required to make a level. The Town tileset looks like this:
I use Tiled to lay out all of the levels (as well as create the levels themselves). Tiled requires an external editor such as Photoshop or MSPaint.
You may also find Pyxeledit useful, as it combines Tiled and Photoshop into one application.