How are the plants in these pictures properly spaced (details)?

So, I love looks like this or this in gardens. However, I thought plants were supposed to get, well, basically at least half a foot of room all to themselves, and I see quite a lot of pots packed pretty tightly. So, how do all these survive without choking each other? Do you really need to give plants so much space, or can you pack them in tightly like in the pictures?