First of all, I don't have much experience on game development but I do have experience on development. I do know how to make a map, but I don't know if my solution is a normal or a hacky solution. I don't want to waste my time coding things, and realise they're utterly crap and lose my motivation.

Let's imagine the following map. (2D - top view - A square)

X: 0 to 500 Y: 0 to 500

My character currently stands at X:250,Y:400, somewhere near center of 100px above bottom and I can control him with my keyboard buttons. LEFT button does X--, UP button does Y-- etc.

This one is kid's play.

I'm asking this because I know there are some engines that automate this task. For example, games like Diablo 3 uses an engine. You can pretty much drag drop a rock to map, and it is automatically being placed here - making player unable to pass through/detect the collision. But what the engine exactly does in the background? Generates a map like mine, places a rock at the center, and checks it like:

unmovableObjects = array('50,50'); //we placed a rock at 50,50 location

if(Map.hasUnmovableObject(CurrentPlayerX, CurrentPlayerY))
{
     //unable to move
}
else
{
     //able to move
}

My question is: Is this how 2D/Isometric maps are being generated or there is a different and more complex logic behind them?