This is part three of a five part series called Mapping Caves, where the basic steps to underwater cave cartography are outlined in a way that both divers and non-divers alike will understand. To start at part one, click here.

Introduction

A stick-map is literally a map of the guidelines – it functions to some extent as a navigational aid, but it tells us nothing about the actual cave. Is the guideline running through the middle of an enormous tunnel, or a passage so small that it would require a diver to remove his tanks to go through?

The second step to underwater cave cartography is to sketch the details.

With the survey completed, a cartographer can use the stick-map as a frame to draw the wall and floor details of the cave passages.

Printing the Stick-Map

Using cave survey software, such as Walls, the cartographer will separate sections of the stick-map to be printed onto waterproof paper over a grid, which helps the cartographer draw to scale.

While swimming along the guideline, the cartographer will artistically draw the walls and floor details around this printed section of their stick-map.

Distances to the walls from the guideline can be estimated in smaller passages, measured using a tape measure, or by running additional lines along the walls that can be surveyed and attached to the stick-map. Handheld sonar devices meant as depth finders can also help cartographers estimate wall distances, but the wide sonar beam of these devices makes interference with cave features such as speleothems a frequent problem.

What do I draw?

Caves can vary so widely in features that cartographers must face a difficult decision at this step: they must choose the level of detail appropriate for their map.

Additional details are always useful, but a cartographer must balance the mandatory information with the secondary information based on the scale and purpose of their map. Remember: the majority of cave maps are made to be used by cave divers for dive planning.

Let’s take a look at the three levels of detail common to underwater cave cartography:

How long does it take to sketch underwater?

Depending on the complexity of the cave passage, most cartographers can sketch approximately 80 to 120 meters per hour but this does not include swim times to and from the sketching location.

For a system like the one shown in part one of this series, the cartographers had to swim up to 90 minutes each way to their sketching location to reach the ends of the map. In total, that particular project required approximately 50 hours of underwater sketching but this does not include the time spent exploring and surveying the cave.

This sketching process takes place section-by-section throughout the cave until the system is finished.