If you missed the first two posts in this series, you can check them out here:

Geography for Worldbuilding, Part One
Geography for World-Building, Part Two: Climate, Weather, and Biomes

When I drew my very first fantasy map, I knew it needed water. My world was a continent surrounded by an ocean, but I wanted bodies of water on the mainland too. I drew a couple big lakes, then added rivers. The most important thing I did right was having my rivers begin in the mountains and end at the coast. I also managed to have smaller rivers join together into a bigger river as they headed toward the ocean. That was a happy accident. I don’t think I really understood that rivers don’t fork into separate rivers. They join.

Where you place your rivers on your map is not as important as where you start and end them. Rivers begin in high altitudes. That means they start in the mountains and they head toward lower ground. This is primarily gravity at work. In the mountains, rivers start out small as brooks, creeks, and streams. As they travel downhill, they move very fast due to the steep gradient. They join with other creeks and streams and form rivers or flow into bigger rivers. Some will even flow through lakes. When deciding the placement of rivers on your map, do take into consideration whether or not you’ve added any rain shadows. Rivers will be more plentiful on the side of a mountain range that gets more water.

Once rivers reach flat land in a valley, they slow down, widen, and curve back and forth. The older the river, the more it meanders. This is due to obstructions on land like hills and rocks, the amount of sediment the river carries downstream and dumps, and the fact that river water flows faster on the outer bends. Subtle curves over time grow, eroding riverbanks more and more, creating exaggerated bends and sometimes canyons. Oxbow lakes can form, which is where a river curve becomes so pronounced that the stream of the river eventually cuts a new path, changing course and leaving a body of water behind. Oxbow lakes tend to form when rivers are high from excess rain.

As rivers nears oceans, the gentle slope becomes almost flat. Here rivers tends to be at their widest and deepest due to the volume of water. Where the mouth of rivers meet the ocean, deltas or estuaries form.

When river water comes into contact with the water in an ocean or lake, it loses energy and deposits the sediment it was carrying. The water keeps coming, though, and as it does, it forms paths in the sediment. These are called deltas. There are three main types of river deltas: arcuate, bird’s foot, and cuspate. The shape of each delta is determined by the strength of the river, the waves, the tides, and which one dominates in that particular area. I drew this image to give you an idea of what each might look like on your map.

An arcuate delta is dominated by the ocean’s tide. The waves hit the delta head on. This causes a spread out, fanlike delta with channels and islands perpendicular to the coast.

In a bird’s foot delta, the river’s flow is stronger than the waves and tides. This means that the river pushes the sediment farther out from the coastline, forming a claw like shape. These types of deltas often occur when a river dumps into a sheltered inlet where the waves and tides are weaker.

A cuspate delta is usually formed when sediments form along a straight coastline. Here the waves are the strongest and push back onto the coastline in opposing directions, creating a pointed shape.

Estuaries form when rivers pass through igneous rock, which does not erode easily. This type of rivers doesn’t carry any sediment. When the river water meets the ocean, the freshwater flowing into the saltwater without any sedimentary obstruction creates a coastal body of brackish water, which is a mix of fresh and salt water. This may happen at a coast or an inlet.

Now, let’s briefly go over the geography of some other water types. Oceans are large bodies of salt water that divide continents. Seas are large bodies of salt water within ocean but that are also partly surrounded by land. Inlets are indentations in shorelines. There are many different kinds of inlets.

A gulf is a large body of water surrounded by land on three sides with a relatively narrow opening. Bays are smaller than gulfs and have a wider mouth. They are also surrounded by land on three sides. Sounds are larger inlets than bays but less protected by land. Some sounds have islands inside them. Smaller than bays are coves, which are often tucked inside rocky headlands. A fjord is a narrow, long inlet between high cliffs. And a harbor is a body of water along a shore that is protected from wind and rough water and deep enough for ships to moor.

Lakes and ponds form in various ways. Plates in the earth’s crust can shift or collapse and form basins that fill with water from rain or receding glaciers. Landslides can block off rivers, creating pockets of water that form new lakes. Meanders can become cut off from rivers and form oxbow lakes. Flooding in rivers can cause new lakes to form. Humans can also create manmade lakes.

I always thought the difference between lakes and ponds was based on size alone, but as it turns out, the difference is about depth. A lake is deep enough that the sunlight cannot reach the bottom while a pond is shallower, in that the sunlight can reach the bottom. If a pond were to grow so cloudy that the sun couldn’t reach the bottom, it would then, technically, become a lake.

A lagoon is a small lake formed near the coast and separated from the ocean by reefs or a sand bank. A swamp is a forested lowland covered in stagnant water. A swamp with no trees or forest is called a marsh. Marshes are dominated by grass and cattails. They tend to be very muddy. Swamps and marshes are usually near a river or lake and are fed on and off by surface and groundwater. Bogs are similar to swamps and marshes but they cannot support large plant life. Bogs usually form where lakes or ponds used to be. They are covered in moss and rely on precipitation rather than runoffs.

I hope that these three posts on physical geography have given you a deeper understanding of how land forms and a myriad of ideas for your next bookish map. I know I’m ready to pull out the map for my work in progress and give it a major overhaul.

Did you learn something new from these posts? Which geographical feature are you wanting to add to your next bookish map? Share in the comments.

Jill Williamson is a chocolate loving, daydreaming, creator of kingdoms, and the author of several young adult fantasy novels including the Blood of Kings trilogy. She loves teaching about writing. She blogs at goteenwriters.com and also posts writing videos on her YouTube channel and on Instagram. Jill is a Whovian, a Photoshop addict, and a recovering fashion design assistant. She grew up in Alaska without running water or electricity and now lives in the Pacific Northwest with her husband and two kids. Find Jill online at jillwilliamson.com or on Instagram, YouTube, Facebook, Pinterest, and Twitter.