To Zoom in or out, press the [Enter] key.
When you zoom in from the wilderness map, you start on the center tile of the local terrain map. When you zoom back out, it saves your location on that tile. From that point, when you zoom in on that particular wilderness tile you will start on the local terrain tile that you zoomed out from last.
At the top of your screen, centered above your map, is a terrain indicator. It shows your current terrain on the local terrain map (Coniferous Forest, River, etc.). If you are standing on the bank of a river, even standing on ground, you may be considered in the river terrain. If you zoom out from a water terrain type it will not save your position, and you will zoom back in to the center terrain tile.
So, if you built a shelter next to a body of water for convenience, and find that you always have to walk to it from the center of the local terrain map, just take a few steps away until the terrain indicator no longer shows a water terrain type before zooming out.
If you are on your raft, in the water, on a local terrain tile and zoom out you will still be on your raft in the wilderness map. If you zoom in from a water tile in the wilderness map, you will be on the center tile (or last tile you zoomed out from) of the local terrain map of water. If you zoom in on a land tile in the wilderness screen, you will be on the center tile of the local terrain map of land... with your raft and any supplies you may have stored on it.
So, unless you want your raft piled with logs to be transported to the middle of a land tile, don't zoom in from a wilderness land tile while on your raft.