Hello denizens of gamedev.net. I come in peace. I am here to mingle with my fellow recreational software creators and perhaps to learn some things about life. 

Right now I am working on a 2D isometric game along the lines of factorio. 

Have you noticed that in games like factorio, age of empires, and basically every 2d isometric game that buildings are placed in a grid of tiles wheras units can move freely between the tiles?

Is there a good reason for that being the standard? Are there any games where buildings or even terrain is not bound to a grid structure? What would be the advantages of the grid? 

One advantage I can think is that it would be easier perhaps to randomly generate terrain on a grid rather than freely. 

Also, can someone please direct me to someone good resources on how to generate procedural maps and also how to save those maps to files. 

Thank you. 

There are a number of reasons why buildings (at least historically) must be placed on grids.

• The game uses a tilemap.  This makes everything very fast to render because you don't have a huge list of objects with positions, graphics to display, etc.  All you have is a grid and on each grid which graphic needs to be displayed.  It makes things very simple and saves on quite a lot of memory, at least for machines in the 90's and before.
• The game logic is easier that way.  In order to place a building in Age of Empires, it must be on an empty space and have land under it, or a dock must be half on the water, etc.  Checking for building placement becomes a lot easier if it's done on the tilemap.  It didn't have to be, but I think we practically every RTS game of the era all the developers just decided it was easier that way.
• In Age of Empires or Factorio, this basically makes walls and conveyor belts possible.  If you could place wall or belt segments independent of the grid, it would be a nightmare to build.  Imagine building from 2 directions and having them not meet up in the middle.  Imagine a unit sneaking through because your wall was a tiny bit too far from a building.  It would massively complicate the game for no good reason so, again, just place them all on the grid.

Can you think of any examples of a 2d isometric game without grid based buildings and terrain?