Mapping - GIS

Map of a huge caldera in the NE Lau Basin, created from multibeam data processed with GIS software

Map of a huge caldera in the NE Lau Basin, created from multibeam data processed with GIS software.

A GIS (geographic information system) is an unconventional tool for ocean exploration. It is neither a physical device nor a submersible technology that comes into direct contact with the water. A GIS cannot take us any deeper into the oceans, but it can take us further in terms of our understanding, because of the way it gathers and analyzes information. Given enough data, a GIS can, in fact, create a virtual ocean inside of a computer.

Geographic features in a GIS can be created in raster data form.

Geographic features in a GIS can be created in raster data form. Click image for larger view.

Geographic features in a GIS can also be created in vector data form.

Geographic features in a GIS can also be created in vector data form. Click image for larger view.

A GIS is comprised of three parts: spatial information, special software, and a computer. These components work together as a system to provide a digital platform for viewing and processing layers of spatial information. Because of its power and speed, GIS technology is doing most of the cartographic (map-making) work that, in the past, was laboriously done by hand on paper charts and maps.

Most GIS users have a working knowledge of classical concepts in Earth-map relations, including geodesy, map projections, and scale, reference and coordinate systems. Earth-map relations determine how a three-dimensional Earth is displayed on a two-dimensional map. Most GIS users also appreciate the importance of understanding the spatial data that they use. Ultimately, GIS users themselves are responsible for imperfections in the digital worlds they create, and the analytical errors that can result.

How to Build a World

As a GIS user, the first thing you see when you start the computer is a blank white screen. Imagine this blank GIS world not as empty space, but as the surface of the Earth, with all of its features and various phenomena "turned off." Your job is to carefully add features to your digital world, one at a time, and stacked into separate but overlapping layers. The unique analytical power of a GIS comes from its ability to find relationships between these separate but overlapping layers of information.

As a GIS user, you can manage the tools of ocean exploration in much the same way that a conductor leads an orchestra. A conductor manages the unique sounds produced by a number of different musical instruments so that they blend together into a rich, multilayered symphony. Likewise, a GIS user manages unique spatial information produced by a wide variety of ocean-sensing instruments, such as satellites, buoys, sonar, submersibles, traps, trawls, underwater cameras, and other devices, until they be combine to form a multilayered reconstruction of geographic reality.

GOES-3 Satellite.

A GIS can be a lifeless digital skeleton of a world without enough good information.

GOES-2 Satellite before launch.

With enough good information, a GIS can be a virtual world.

Types of Data

A GIS has two very precise ways of creating geographic reality in digital form. They are called raster and vector data structures. A raster data structure reconstructs geographic reality with a multicolored surface of cells of uniform size, shape and spacing. Raster grids work especially well to represent base features that vary continuously over the surface of the Earth, such as bathymetry or sea surface temperature. A vector data structure reconstructs geographic reality into a stick-like skeleton of interconnected points, lines and polygons. Vector frames work especially well to represent features that have unique shapes such as political boundaries and coastlines, as well as networks of linear features, such as rivers and highways.

The most important element of reconstructing geographic reality in a GIS is good spatial information. If the spatial information you provide to your GIS is sparse or of poor resolution, then the world you create inside your computer will be a lifeless digital shell -- a sharp contrast to the complexity of a living earth.

Exploring a Virtual World

With enough good information, a GIS can become a virtual ocean in itself. In this virtual ocean world, you can explore the depths in every way imaginable, just by clicking around with your mouse. You can strip away trillions of gallons of seawater and gaze at giant underwater cliffs at the bottom of the Gulf of Mexico (as in the image on the right). You can transport yourself to the Florida Keys National Marine Sanctuary at light speed to scan the plethora of the different types of tiny plants and animals that flourish on the sea floor. You can also use a GIS for analytical applications, such as determining potential habitat for a certain species by identifying all areas shallower than 100 m, further than 10 mi from the nearest urban area, and within a certain range of sea surface temperature.

This Landsat image depicts Pearl and Hermes Atoll.

The Gulf of Mexico in 3D perspective. A GIS can create very accurate and realistic-looking environments. Click image for larger view.

If the ancient Roman gods had computers, Neptune would have been a GIS specialist. A GIS can take all that is known about the seas from direct observation and measurement, and create a digital ocean world that one has the power to control. For many people, the GIS is indeed a godsend, because exploring the oceans on a computer is the only means they have to visit the alien and largely inhospitable world that lies beneath the deep blue sea.

The Web team gratefully acknowledges this contribution by Robert Aguirre, a geographer in NOAA's National Ocean Service.