INTRODUCTION TO GIS (V)

Time has passed since my last post on GIS, sorry for the waiting. But here we are on track again, this time with an essential one… how to add the points from your GPS to your map. Remember you can download all tutorials from my Academia.edu page. Enjoy!

Vector points:

So now that we have our raster map of the region we want to study it is time to add some sites to it. In order to do this we will create a vector map from a list of points in a spreadsheet.

1.- Once you have a list of points you can organise them in a spreadsheet file like this:

GIS 5-1

The most important things to take into account are the order to the fields, which is not mandatory but strongly suggested, and that in order to avoid issues it is better to avoid spaces at least on the headers. This is a simplified version from my Ph.D. research, and it gives you the general structure. We need only three main fields, the two coordinates and the CAT, which is just a field from 1 to n, like the index on a database. Names, types of sites and many other fields can be added after this. It is up to you include as many as you want, but for the lesson of the day we will use this simplified version.

2.- Now it is time to save it. We need a .csv file, so be sure you save it in this type. You will be requested to indicate some delimiters as Field delimiter (a comma , ) and Text delimiter (a doublequote “). This information will be important and necessary in the following steps.

GIS 5-2

3.- Open GRASS and load your base map. This will be the background in which to display your points.

4.- In File ~> Import Vector Data ~> ASCII points or GRASS ASCII format. In the pop-up menu browse the csv file you want to use and create a name for your map.

5.- In the Input format tab, select Input file format point, Field separator comma and Text delimiter doublequote.

GIS 5-3.png

6.- In the Points tab be sure the Number of header lines is set to 1, the Number of column used as x coordinate set to 1, the Number of column used as y coordinate set to 2 and the Number of column used as category set to 3. These numbers indicate the software how the information is organised in the .csv file. Press Run.

GIS 5-4.png

7.- And here we go! X marks the spots. Of course you can change shapes and colours, organise the points by types, but we will leave all that for another day, Right now just go outside and find as many points of your working are as you can. We will leave the aesthetics of the map, which are also very important since they make your data comprehensible, for another day.

GIS 5-5.png

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