This generator is ideal for making dungeon maps – tight collections of well defined rooms connected with corridors.
The map number is used as a seed for the random number generator. The seed can be anywhere from 1 to over 2,000,000,000. (That's billions!) Multiply that by the two different Layout styles, three sizes, and with the combination of colours and tile types you have a near-limitless number of options.
First, a layout is created. With the Fancy Rooms layout this uses a hand made library of room designs as well as a set of simpler designs generated by the system. These are randomly selected for placement on to a grid, starting with the entrance. An algorithm then connects rooms together. For the Simple Sprawl layout square and rectangular rooms are randomly placed on the grid and then joined by corridors.
Once a layout has been created the image is built by assembling and then combining various layers for the base, tiles, shadow, walls, and doors.
The original dungeon map generators used lower resolution graphics and different techniques to build the initial map. If you prefer the old generators they are still available but this new generator has more features and options and makes higher resolution maps.
There is a lot of large image manipulation that has to go on to make a map image. For the largest image size this can be hundreds of megabytes of data in memory. Processing that can take a moment, but good things come to those who wait. The preview images load more quickly than the higher resolution downloads.
Unfortunately not. The way in which the code works is part of the "special sauce" that makes Gozzys.com work. The good news is that you can reuse the maps that are produced under a Creative Commons license.