Thoughts on Coastlines

Featured Image: Philippines with Stamen Watercolor Theme

You can tell a lot about a map by how it’s coastlines are displayed. A simple map will only have a simple line and maybe a blue color fill to delineate the land from the water. However, artisan cartographers approach coastlines a place to highlight their attention to detail. This is probably why I’m always drawn to the coastlines on well-made maps: there are subtleties that enhance the aesthetic of a map.

Like a detailed and intricate compass rose, the coastline is a place where an artist can leave her mark. There are many ways to display a coastline and I would like to look at a few.


Subtle Delineators

Oftentimes the separation between land and sea is not the focus of the map. In these cases maps will use fine lines or gentle gradients to show the coastline. The sea and land will sometimes even be the same color.

From a map of the Great Lakes by Daniel P. Huffman

Daniel P. Huffman, a cartographer who often writes about coastline aesthetics, often plays with these subtle lines. Notice how the lines get thinner and more spaced the further they move into the water.

Highways of Australia Metro Map by Andrew Douglas-Clifford

The italic font used in the name of the body of water also underscores the separation. One of my map-gazing pleasures is seeing a nice italic font used for water. It’s a mark of distinction between amateurs and professionals.

I also like this tube style map of Australia by Andrew Douglas-Clifford. The land mass is a gentle shade of gray, the coastline is a thick white line and the ocean is a familiar light blue. Unless you’re looking for it, the coastline isn’t noticeable. In the hierarchy of a map this crafted subtlety is important


Inner Glow and Gradients

Some other aesthetically pleasing mapping conventions are the inner glow and gradients on bodies of water. The inner glow, or sometimes called a coastal vignette, is a way to fade the water out from the land. Again this is subtle but pays dividends in the overall aesthetic of a map. Anybody can make a map with modern software, but it takes a discerning eye to make it art.

From a map of Tasmania by Dan Bowles

This excerpt of a map of Tasmania by Dan Bowles is an example of the inner glow effect. The eye naturally focuses on the land. The slight darkening of the blue as it moves further from the coast implies the increasing depth of the open sea.

The inner glow can be created by using buffers, offsetting or using a raster with calculating Euclidean distance from the nearest landmass.

One of the problems with this method is that it gives the impression that it represents the depth of the water off the coast. It is not, and is only a stylistic flair.

Wilson’s Creek National Battlefield Map

Another style element is the use of gradients. This is useful for local maps to give the impression of the reflection of the sun. It is surprising that many cartographers don’t use this simple addition to their maps.

One of my pet peeves is that there are too many maps that use the bare basics. It is so simple to make maps with modern software. Just push a button and the software spits out a map. Within seconds the user can post that to /r/MapPorn and not give it another thought. It doesn’t have to be that way. The digital map is a canvas: an opportunity for anyone to express their artistry.



Detail from Mapa de los Paisajes de Cuba by Erwin Raisz and Geraldo Canet

Bathymetry, the study of the underwater depths, is a more accurate way to distinguish the land from the sea. These maps get to the core of why maps are so pleasurable: they uncover the world in a way that is intuitive. Unlike the inner glow and gradient maps, these maps have the imprimatur of scientific accuracy.

Detail from a contour map by Professor Kitiro Tanaka

These maps often use one of my favorite elements: Tanaka Contours. This is a way to show relief contours (on land or undersea) by simulating light from one direction. The contours facing the light are white or light colored, while the contours facing away from the light source are darkened.

While these contours are separate from the coastlines per se, let me just remark on how exquisite and subtle this effect is. Whenever I notice a map with Tanaka tours I am immediately impressed with the knowledge that this is no simple quick map, but a work of art that someone put a lot of work into.



Old-Timey Coastlines

From Hollandia Nova by Melchisédech Thévenot (1644)

Antique maps have beautiful, meticulously detailed coastlines. They are often drawn with offset lines radiating from the coast or parallel lines that fade in and out as they move away from the coastline.

These maps were often reproduced with intaglio and flat plate engravings. That work itself is an art that is easily forgotten in the modern age of computer aided drawing software.

From Ile de St. Domingue by August Henri Dufour (1859)

Appreciating these maps is worthy of more contemplation than a simple blog post. However they are something to look for when looking at antique maps.

The radiating coastlines are especially palpable. They imply the liquid state of the ocean and how easily a ship can plow through the waters. They also give an idea of distances to the center of two land masses, with implications on the separation of boundaries between administrative authorities.


OpenStreetMap Style

OpenStreetMap Detail of the North Coast of Taiwan

While the OpenStreetMap (OSM) does not have the flair of the previous styles it is distinctive and deserves some thought. The OSM tile set includes is practical and functional. It includes features like territorial water boundaries and natural marine preserves. It is rare, in fact I can hardly think of any other maps that include these features. Of course while they may give the air of authority, it would be foolish to think they are authoritative at all.

One could easily think of multiple places around the world where there are disputes over water boundaries. The tension over the South China Sea are especially relevant. There are even a number of disputes between friendly countries like Canada and the United States.


Generalization of Coastlines

Styles aside, there are going to be differences on the representation of coastlines. Two maps may have palpable differences in the coastline and both be correct. Some charts will use a mean sea level to represent the coastline, while others will use sea level, and yes they are different. Mix in with that the changing climate and dynamic nature of eroding coastlines and there is no such thing as a static coastline.

Further Reading