I call map weight the size of your map file. Players don't want to spend time loading a map, so you want to have a light map. From my point of view, no map should be bigger than 300kb, otherwise, there is a problem somewhere. The average Minisiege map is 150kb. Decreasing the weight of your map is easy, but mappers usually don't know how to do that.
When you start with a virgin map (open any map, delete all props and reset the terrain), your map weight is 0 kb.
The following modifications will increase your map weight:
- Modifying the height.
- Modifying the terrain texture or color.
- Adding an AI mesh (path for bots).
- Adding props (objects).
People tend to think that props are the most heavy modification but that's totally wrong. Modifying the terrain will drastically increase the weight of your map. Therefore, your aim is to limit the modifications made to the default terrain. As a matter of fact, it's especially important to start a map with the appropriate size (no useless ground!), the appropriate height (don't start with a mountain map if you want to have a plain!), the appropriate polygons number, and the right default texture (don't paint desert on a plain map!). For this, follow the instructions on how to use the Terrain code editor. As for AI meshes, those are quite heavy if you mesh the whole map, so don't do that unless you really intend to have bots on your map.
And of course, don't spam useless stuff!
I call map performance the impact of the map on your FPS. It's very likely that props with many textures and polygons (the elements composing a 3D object) will be more laggy than others. Objects like trees, some houses, are very unfriendly props and shouldn't be spammed. In addition, dynamic props like smoke or fire can cause lag, especially when particles are involved. That's also true for special effects like rain, fog, and snow to a lesser extent. So I would advise to avoid using those effects unless your really deem it necessary. Keep in mind that you will rarely feel the lag while mapping, because you are alone on your map. But if dozens of players join it, the number of polygons will sharply increase.