Once we start thinking in terms of large, complex maps editing the map by hand becomes a daunting task. Instead, we want a tool to edit the map visually. One of the best free tools to do so is the Tiled Map Editor. Tiled is free, open-source, and widely used in the games industry. It allows you to quickly create a tilemap by importing tilesets and drawing the map using a suite of visual tools. You can read more about Tiled and its functionality in the documentation and covered in this video series by GamesfromScratch.
However, it adds additional concepts to tile maps that we have not yet discussed.
Because Tiled is intended to be usable in a wide variety of games, it allows properties to be defined on almost everything. In Tiled, properties are simply key/value pairs, i.e. "Opacity" might be set to 0.5. There are no pre-defined keys, instead you decide what properties you need for your game. The properties are stored in collections, essentially a Dictionary<string, string>, which is how we’ll interpret them in our C# code.
Tilesets are implemented in a similar fashion to our earlier discussions, however:
Instead of a single 2d array of tiles, Tiled allows you to create maps with multiple layers, each with its own 2d array. This can be used in a variety of ways:
Conceptually, a map layer is implemented the same way as the simple tile map we discussed earlier. It is a 2d array of tile indices implemented as a 1d array, along with storing the width, height, and any properties that apply to the entire layer.
In addition to layers of tiles, Tiled also supports image and object layers.
An image layer represents an image that is not a tile. This can be used for large bitmaps that cover the entire layer, or smaller ones that appear in a particular spot. Images can also repeat to fill the layer or defined space.
In addition to tiles, and images, Tiled allows you to place “objects” in a map. These are represented by boxes that do not correspond to the grid system of the tiles. Objects are simply a rectangle plus properties, and can be used to represent anything you need to place in the game world - spawn positions, event triggers, doors, etc.
Objects are organized into object layers, which are essentially a collection of objects.
Tiled uses an XML file format, TMX. Thus, you can load a TMX file and then parse it with an XML parsing library. In fact, Tiled was released with an example engine that does this, created by Kevin Gadd. This was later converted into C# for use with XNA by Stephen Balanger and Zach Musgrave.
I further converted this for use with the current version of MonoGame, with additional documentation. It can be found on GitHub.