Good morning interweb
Let's worldbuild
Fantasy Maps & Plate Tectonics
Earth's crust is broken up into fragments
Carried Convection currents in the upper mantle these fragments AKA “tectonic plates” move relative to one another
As a result, various landforms are created at the boundaries where these plates meet
Which landforms exactly? Well, that depends on what type of plates
we got and what direction they're moving in. Plates can either be continental or oceanic
Continental plates are thick, felsic in composition and have relatively low densities, whereas oceanic plates are thin
Mafic in composition and have relatively high densities. Plate boundaries come in three flavors:
Convergent–plates coming together
Divergent–plates moving apart
and Transform plate boundaries–plates sliding past one another
An Oceanic-continental convergent boundary looks like this as the plates collide the denser oceanic plate is forced under the more buoyant continental plate
As the plates collide the denser oceanic plate is forced under the more buoyant continental plate
Features created here are subduction zones AKA deep ocean trench, earthquakes, mountains and volcanoes
Think the west coast of South America
An Oceanic-oceanic convergent boundary looks somewhat similar except everything's happening underwater
expect to find ocean trenches, earthquakes, smallish mountains in the form of island arcs and volcanoes
Think the Philippines
The final convergent boundary is Continental-continental
here both plates are composed of buoyant rock so neither will want to fully subduct
Causing a lot of folding, faulting and buckling which will lead to the creation of very big mountains and a ton of earthquakes
Think the Himalayas
Then there's the two divergent plate boundary subtypes
Oceanic-oceanic divergent boundaries look something like this. As the plates pull apart
they get thinned out and rising mantle material posture plates upwards forming a ridge
magma will begin seeping out of the fault line and will form new crust
Expect to see a mid-ocean ridge aka an underwater mountain range with a Rift Valley at its crest
earthquakes and, where the ridge pops out of the water, volcanic islands. Think the mid-atlantic ridge
And the Continental-continental divergent boundary is kind of the same thing, except everything's happening on land
Think the East African Rift Valley
Now in theory you could have an oceanic-continental divergent boundary
But given that new crusts created at divergent boundaries your oceanic-continental divergent boundary will quickly become An oceanic-oceanic boundary
And finally the two transform boundary subtypes. The most common example of a transform boundary is continental-continental
Think the San Andreas Fault
expect earthquakes
Oceanic-oceanic transform boundaries are kind of cool. They occur alongside divergent boundaries
If we look at the Mid-Atlantic Ridge we see that the divergent boundaries are offset at intervals by transform faults
This happens as a natural consequence of plate motion around the sphere and like before
expect earthquakes
So there you go all the plate boundary subtypes and their associated structures
Bear this table in mind because we're going to use this information to create a believable fantasy map
Planets are three-dimensional objects
So I like to map in three dimensions. Many fantasy maps look great in 2d
But look weird when projected onto a sphere. As such my method requires two main programs: Photoshop and Gplates
That said you could just as easily achieve everything
I'm about to do by drawing on a piece of paper and a ball
So I'm not going to give you the specifics of each program. I'm just gonna give you my workflow
I like to start off with an initial concept
In this case, I'm gonna aim to create a Pangea-like supercontinent
Situated mainly in the northern hemisphere of my planet that has just begun to break apart
aside from being limited by the dimensions of a piece of paper, fantasy cartographers often inadvertently create Earth clones
Which is fine if that's what you're after
But I'm not and this brief will prevent me from replicating Earth
Next I create an equirectangular map of my world, that is to say I go to Photoshop create a two-to-one aspect ratio
document and overlay a twelve by six grid on it. Before proceeding it's worth noting
What distortions are present in an equirectangular projection. Namely, the closer you get to the poles the more squished and elongated things will become
So with that in mind
I'm sketching my plate boundaries until I get something that looks like this
For reference, Earth has about seven to eight major plates, about ten minor plates and a ton of micro plates
Also, Be aware that your left and right edges will need to match, because we're going to wrap this around a 3d globe in a bit
And try to ensure that no more than three plates interact at any given point
In practice this means that all interaction points must either form single lines or T shapes
not crosses
Links in the dooblydoo to a paper on this
With the plate boundaries in I go to Gplates and check to see if everything looks good in 3d
Particularly at the poles. If needed I do a bit of editing directly in Gplates
Until I get something that looks like this. I fixed the poles and got rid of a few plates
I thought weren't necessary. From here I mark in which plates would be continental (shown with a dot) and oceanic (no dot)
This is not to say that the dotted plates will be all land
Rather they'll be predominantly land and vice versa for the oceanic plates
Remember, earth-like planets will need most of their surface to be covered in water, so pro tip: make your biggest plates
oceanic, like the Pacific. Next I mark in the main direction the plates will be moving best way of doing
this is to find where your planets mid-atlantic ridge will be. The location where two or more major plates are separating. And try to imagine
how all other plates will move in relation to these
Here's what I came up with. Basically these fellas are separating, giving rise to a fledgling
Mid-ocean ridge and are being met with resistance from the north and south
Awesome! Now the fun part–filling in the continents like so. Zero artistic ability needed here
We're going for function over form and anyways. It's not like there's a shortage of YouTube tutorials on the artistic side of mapmaking
With the continents in I now know exactly what's continental crust and what's oceanic crust so I begin marking in what's happening at each boundary
Remember plates don't just move side to side and up and down they also rotate
Which means the plates can be moving in different directions in different areas
So any conflicting directions here can be chalked up to rotational movement as long as it's consistent
Also there definitely will be places where you'll be unsure to what's going on
Don't worry that is entirely natural. Expect some boundaries to feature a mixture of boundary types at various points depending on their shape
Based on the landforms, I expect to see at each boundary
I go ahead and throw down various islands. Islands can really help sell the believability of worlds
So don't skimp on this stage. Note that I haven't included any coastal islands because we're focusing on place tectonics, but you
totally should. More islands the merrier
Oh and make sure to include some volcanic hotspots
Hotspots are not tied to play boundaries and can occur anywhere on a plate in the ocean hotspots will give rise to
volcanic island arcs
Magma breaks to an area of relatively thin crust and a volcano is formed as the plate moves over to hotspot newer volcanic islands will
form and the older ones will cool subside and erode forming older smaller islands and atolls
Think the Hawaii Island chain
FYI hotspots can also develop under continents forming large calderas. Yellowstone is a good example of this
So let's go with a Hawaii-like island chain here
And boom. Map done.
To finish off, I bring this back into Photoshop and create an elevation map to show where my mountains will be
Note that I've also included the continental shelf the area of seabed around the landmass were to see is relatively shallow compared with the deep ocean
As Aaways, I use the table and the plate boundaries to guide me. As a final option step
I use G projector, another free, cross-platform application, to make an export. Many many many
Many many many many different projections of my world
Here, have a heart shaped map as a thanks for listening to me expose the virtues of tectonically formed fantasy
cartography
Good morning interweb. So, if there's any interest in me doing an in-depth tutorial on how to use Photoshop
and Gplates, let me know in comments. Just be aware that that would mean some very lengthy
very screenshare-style videos, so I need to know if you're cool with that before I go ahead with it. As always
Thank you so much for watching and special thanks
go out to Isaac Silbert
Andrew Chehayl, Robin Hilton, World Anvil and Ripta Passay. You folks are all of the awesome
Thank you, and until next time. Edgar out