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    Amy
  Mon Nov 25, 2013 12:05 pm
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I'm sure everybody has done history and geography at some point in school, but for those who haven't, or those who just forget when it comes to designing, writing, and mapping out their games, I thought a good idea for a column in the eZine would be a look at RPG gaming from the perspective of both. Now, I took History at A-level, and Geography at GCSE, but the things we learned were certainly useful enough to apply to a game – designing coastlines, kingdoms, and even weapons for the character to use.

So I want to talk about rivers. While you might think it pedantic and a waste of time to spend time designing them properly, it can actually lead to some interesting land formations that otherwise might not have been thought of, making maps much more interesting and that little bit more realistic.

The first thing to cover is what a river actually is: a path formed by water as it flows from a high point to a low point. Actually, the river itself only really becomes a river when several streams meet one another in a significant flow, but the furthest one of these streams can be said to be a continuation of the main river. Basically where you have some land higher than some other land, any rain which hits the land will take the quickest path it can downhill – but only ever downhill and cannot climb along the way. It will follow any route it can to do this. The area in which all water flows into this one river is called the watershed of that river.

So at our beginning, at the source of each individual stream, we have small flows of rainwater sliding down a hill slowly trickling, until it meets more water and becomes a solid stream. This stream, as it moves, picks up rocks and moves them gradually along the surface of the ground. This seems insignificant to begin with, until we realise that over hundreds, thousands, millions of years this causes erosion that eventually leads to great canyons. Normally where a river is younger, say a few hundred years, all we have is a slightly sloped valley or even just river banks in a “V” shape (these are, unsurprisingly, called “V-shaped valleys”).

I said the water would take the quickest route possible. Not all rock is the same, some of it easier to erode than others, and the ground is not one continuous rock. This means as the water and the rocks it moves erode the land, it does so at different rates, even changing the course of the river entirely as the eroded land allows it to bypass formations it otherwise couldn't – or even making the river several hundred miles longer as the eroded land means it now cannot climb uphill to get back where it was!

Where the land erodes later down the river but not earlier, because of a change in rock types, we get a waterfall. Waterfalls are a vicious circle: as the waterfall gets higher it drops water further so further erodes the land below it. This creates a plunge pool beneath the waterfall that can be several metres below the actual bed of the main river. Gradually the waterfall begins to move backwards as the faster moving water becomes better at eroding the harder rock behind it.

Waterfalls occur where the water moves it's fastest – near the beginning of the river – with some smaller ones mid-way. As the water approaches the coast, further along, it becomes slower but also more powerful.

As the river is met by other streams it gains more and more water, becoming larger and wider. We've now hit the middle of the river and here it takes the form of a sweeping snake, a little slower than the earlier gushing streams.

Here where the land is much flatter the river tends to make sometimes spectacularly meandering turns around the smallest of hills (remember, a river cannot climb, it can only move downhill). You can see evidence of this on a map of Africa, where the Nile turns significantly back on itself part way. This creates more interesting landforms for us to take a look at and incorporate into our games.

In a river bend, the water moves faster on the inside of the bend and slower on the outside, like a running track. This means it erodes differently. The inside of the bend is gradually, but powerfully, eroded, moving the river over quite large distances over time. Eventually where we have a C shaped curve we end up with an O in the river. I mentioned earlier that the water always takes the quickest path: this means that one side of the O will go unused.

Remember all of the rocks we were moving along with us earlier? Well, as the water is slower at this point, the river cannot hold on to them and starts to deposit them – in it's slower places. In the case of our O, it drops these in the larger curve, and on the edges of the main now straighter flow, cutting off our earlier C and just creating a straight line of a river. This C-shaped water body is called an “Oxbow Lake”, and they are very common. The inside of such a lake is a good place to site a town as it's near to the main river, protected by a natural moat, and protected from the river itself moving as it's, for now at least, pretty stable.

Because as it goes along more and more streams will join the river, from the aforementioned watershed, the river gains more volume as it goes along, becoming wider. Eventually it becomes too wide for even bridges across which poses an interesting natural barrier for mapping.

At the end of the river it flows into the sea – and eventually the oceans – called the mouth. This is a good call for placenames around here: historically towns and cities have been founded next to rivers and named after features along them. For example, Exmouth is at the mouth of the river Exe, Cambridge and Ironbridge named after bridges on the course of rivers, and small towns such as Penkridge (river Penk) or Exeter also gain the names from rivers, often corrupted over the years by misspellings or just poor word of mouth.

It's interesting looking at the world maps of some pretty big games and seeing the glaring errors in their rivers – RuneScape comes to mind which has a river with two mouths! - one of them at the top of a mountain. The laws of physics may not always apply in games, but it can be interesting to try and get them right.

I think a lot of RPG Maker rivers suffer the flaw of their rivers being created by autotiles, or just tiles in general. The 32x32 tiles do not lend themselves well to creating rivers which also have smaller streams tricking into them, and waterfalls are difficult to create in large numbers without them being too spectacular in their nature. We can however create the terrain created by rivers: oxbow lakes creating natural moats, large meanders, boulders distributed near the source of a stream slowly rolling down the hillside, and most spectacularly the canyons left behind by rivers many millenia in age.


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