Maps and Software. Creating a Location:
Despite what you might think, the first thing you need to start working with maps is not a computer, a GIS program or some GeoTiffs. The first thing you need is a research question. If you do not have this, the rest is worthless, because your research question is going to condition what kind of analysis you will carry out and how. So, before starting with these lessons I would suggest you to think about your research area and what would you like to know about it. You can be interested on exploring which areas are under the visual control of your site, or the most efficient route between a workshop area and the place where raw material were collected. Every example in these posts can be tried with any map, but if you do not have any specific research area or just want to give GIS a try you can use the maps of the area of Korinth that I will use as an example.
The software I am going to use is GRASS. This is an open source program supported by a community of developers around the world, which include some of the big names in Landscape analysis such as Michael Barton, from Arizona State University. You can download it for free here. Everybody has his/her favourite program, and usually causes intense debates around beers on which is better and why the rest are useless. GRASS is my favourite one for two reasons: first, it is one of the most reliable GIS programs and it is constantly updated by a community of developers. Secondly, it is completely free. Many other programs are very expensive and they do not offer, in my opinion, any analytical advantage over GRASS. It is true that it is perhaps less user-friendly than other programs, but you will see that once you get used to it, GRASS is very straightforward.
A fantastic source for free maps is the website www.usgs.gov. You only need to create an account and start downloading the maps you need. For our example of Korinth we will be using a DEM GeoTiff. The resolution of these maps is 30x30m. If you want to use the same maps of my examples, I have uploaded the file here. Unfortunately, wordpress does not support .tiff or .rar, so I have changed the extension of the file to .pdf in order to upload it here. Once you have downloaded the file just change the extension from .pdf to .rar and extract it.
One final note on these tutorials. As you will see, the software will offer you numerous options to create and process your data. Along these years I have discovered that the best way to teach GIS is to focus only on the information needed to make the maps for each lesson. This way we minimise the noise of dealing with too many options and tags. Other options will be explained when needed.
Creating a Location:
A location is a “georectified folder” a place where all your maps get stored. The difference between this location and a “regular” folder is that it is defined by a region, a geographic area that delimits its boundaries. It is the first necessary step in any project, and although the way of creating a location varies depending on your area of study, we will start with the easiest one: creating a location from a GeoTiff:
1.- Select location wizard. If this is the first time you are using GRASS you will be requested to create a GIS Data Directory. Just select the folder you want using Browse.
2.- Select the names for your Project Location and Location Title. Avoid spaces if you use more than one word. You can use the same name for both, in this example, korinthia. Press Next.
3.- Of all the options, select Read Projection and datum terms from a georeferenced data file. Press Next. Select the file using Browse. Press Next. Now press Finish.
6.-In the pop-up menu select Yes, so the region will be set based on the information contained in the file. Press Ok. In the next pop-up menu select Yes. This will create a new mapset. Different mapsets can be created in your location if you want to keep several map analyses separated.Your screen should look like this.
Opening the Map:
1.- In order to visualize the map, make sure in the main screen that your location and mapset are selected and press Start GRASS.
2.- You can see two windows now. One is the Layer Manager, where you open and manipulate your maps, and the other is the Map Display, where you can visualize the result of your work on the layer manager.
3.- To open the map you used to create the location select in the Layer Manager the icon of Add Raster Map Layer. In the pop-up menu select the map (the only one you have so far) and press. Now you can see your map in the Display.
4.-The colours, however, look a little bit odd. It is a good time to remember now that a Raster map is not a map of elevation. A raster map is just a dataset made out of a series of squared (in this case 30x30m) cells that contain a number. This number can represent many things, and we will make maps with cells that represent seconds, degrees, solar radiation, and many others. But right now we are working with a map that contains data on elevation, and we need to improve its visualization, To do this, we will change the colours of the map.
5.- To change the colour table of the map, select in the upper part of the Layer Manager Raster ~> Manage colours ~> Colour tables. In the new menu go to the tag Define and in the box Name of colour table select, or type directly, srtm. Press Run. As you have seen there are many combinations of colours to choose from; srtm is a good standard to work with, easy to visualise and interpret, but you can choose any colour combination you like.
6.- The only thing left for you is to check the map in the Map Display. Perhaps you have realised that the map is not showing the region of Korinth but the west of the Peloponnese. Indeed, you are completely right. Usually your region of analysis requires more than one single map, so in the next post I will teach you how to import more maps to your location and paste them together into a single map.