We as paddlers are a niche market at best, if your a cheapskate like myself no market at all! This means that there are not many navigational tools available on the market that are all that useful to us. Nautical Charts, arguably one ofthe most important sources of navigational information available (second only to your senses, but that is a whole story in itself) are big, unwieldy and often not in that useful of a scale at all. GIS or ‘Geographical Information System’ is a system to manage and process geographical information using Computers. Using such a system, we can create our own charts and maps, gathering information from various sources. This series of posts is not meant to be a thorough introduction to GIS, but rather tries to point at some of these sources of interest to sea kayakers and mariners, still it is probably a good idea to touch on some basic concepts.
There is a distinct difference between a chart and a map. I will not go in to details, NOAA can explain it much better. GIS does not know of this difference. I will use the terms interchangeable depending on context.
A raster map is essentially a large image (or tiled set of images) representing some information about a certain area. You can think of these as essentially a scan of a paper map. Simple to display, but there is not a lot you can do with it. Zooming gets pretty ugly pretty quickly and referencing anything is a manual affair. Still, they are extremely simple to work with, and it tis what we will use for creating our first charts.
A vector map is something else all together, instead of a picture of a map, think of it as a list of descriptions of features on the map. This has some advantages and some disadvantages. On the advantages side; it offers a lot of flexibility, there is a lot of programmatic processing we can do and we can make the maps look exactly how we want. It also scales much cleaner. On the disadvantage side; the NOAA raster charts are a gold standard people expect and are used to, and the clean scaling does not give a visual indication of the acuracy of the chart at that scale.
QGIS is a free and open source GIS system, you can download it for free at QGIS Download I am mostly a Linux user and not all that familiar with the install on other OS’s, give it a try and if you have any issues I’ll try to help as I can.
Next time: How to get a Chart into QGIS.