Questions about size, rivers and a swamp.

[Raptori]

First I'd like to ask you about the size. How big do you think this should be? (like how many km/miles long from the top to the end?)

In terms of the shape and also positioning of the mountains, it could actually be any size. I'd work out what the scale is by deciding how wide those rivers are. If you decide they're a mile wide, and you know they're 2px wide on the image, then you can easily work out the overall scale of the area.

Would it be possible to put at least 4 kingdoms in this piece of land?

Most likely. It depends on the dimensions of the land, but to be honest it looks big enough for a fair few kingdoms. People usually diverge into separate kingdoms/cultures based on geographical limitations, such as mountains, wide rivers and oceans, or climate boundaries, so it'd be a good idea to adjust the geography to fit the kingdom sizes you want.

What I think myself, is that my mountains are perhaps too big, and that will make the land look smaller.
Do you think, if I would make the mountains smaller, that his piece of land could be a continent?

Yeah the mountains do look pretty big, but then again they're using the style that generally just shows "mountains are here" rather than actual scale, so it could still work either way.

Second, I'm note sure about the rivers. Besides mountains, what can be a source for rivers? And if you let a river come from a mountain, does it have to be a snowy mountain?

I guess you could have rivers originating from a marsh on a plateau (which would be a very interesting ecosystem actually), but it'd still be roughly the same process as mountains. Generally speaking, rivers are most often caused by rain or snow on the sides of mountains. In most cases the rain/snow is caused by moisture being condensed out of the air, which is caused by the air's temperature decreasing as it gains altitude. Rivers therefore generally flow down the windward side of a mountain range.

I'm not sure if my rivers are realistic enough...

They're a little bit off - rivers don't split as they flow towards the ocean, they converge (except right at the end where deltas occasionally form). The general structure can be visualised as similar to the structure of a tree. The trunk is the main river, and is rooted in the ocean, while the branches are tributaries and twigs are smaller streams. Starting at the top, the streams and tributaries (or twigs and branches) converge as they go downhill (since they take the lowest available route), until they're one big trunk of a river that eventually goes to the sea. That's not a complete picture obviously, but it works as a general principle.

But where can you place a swamp? Must it be near the ocean, or not, or must it be near a river. Can it be in the middle of the land, or does it need to be surrounded by water? I tried to google it, but I couldn't get a clear answer. (Perhaps it's my english, idk)

This page should help a lot! So in short, places such as shallow river and lake shores. Basically you can think of them as exceptionally shallow and incredibly slow moving sections of a river - you could even have a river that transitions into a huge swamp which would contain slight, slow moving currents, and then drains out at the other and and continues onwards. Lots of interesting things to do with swamps

Hope that helps, don't hesitate to ask more questions