GIS - Introduction

version française


GIS stands for Geographic Information System and is a multi-purpose tool. It is a platform that can handle different types of geographical data, analyze it and produce a map. In this class, we will use GIS to make a map of the locations where we took our measurements. We will also use this tool to create new data sets.
There are many different GIS systems available but in this course we will use QGIS, an open-source version. We will cover the topic of GIS and the closely related fields of cartography and surveying. As such, this module is just a brief introduction to enable you to create your own fieldwork maps. Thus, the given information is not a deep dive into the theory, but you will find links to pages and literature if a specific topic catches your interest.

The following table lists the three essential steps to produce your map:

Fieldwork During fieldwork, you will collect your data.
GIS This regards lab/computer work. You will import your data from the field, create new data sets, and download data from online resources. Depending on your topic, you can also use GIS to analyze your data.
Cartography This part is included in the GIS work, but we will focus only on the production of the map.


Before we start with the step-by-step guide, we need to cover the concepts of Geographic Coordinate Systems (GCS) and Projected Coordinate Systems (PCS).

GCS are spherical or ellipsoid coordinate systems. They allow your position to be described in Latitude (Lat) and Longitude (Lon). Imagine this as a 3D system. A good example is Earth :)
A GCS tells you where you are on this planet. The World Geodetic system is a widely used global GCS. For now, the WGS84 is the most recent version. For specific purposes, you can rather use local GCS. For example, using a local GCS is important for very precise surveying. Fortunately, the Earth is not banana-shaped but it is also not a simple sphere. The best available approximation of its shape is a geoid, because it allows taking local gravity variations into account. The next table lists two common ways of denoting coordinates in a GCS.

DMS (Degree (°), Minute ('), Second ('') ) 78° 13' 21.37"N ; 15° 39' 4.77"E Think about the coordinates. It is fairly easy to get a rough estimation of the position on Earth just by knowing the Lat/Lon to the degree. This type of notation is great during fieldwork.
DD (Decimal degree) 78.222603 N ; 15.651325 E This expresses the same position, just transformed to a decimal number. It is a little bit harder to imagine where you are but during work in a GIS, this is often the easiest format to import (as you only need to import a number).


PCS projects a 3D GCS onto a flat area. A famous example that is often given: imagine an orange (first a banana...now let’s vary with a citrus!). How can you flatten the peel to a surface? It would require tricky cutting or a transformation of the original shape. Whereas the GCS give you your position on a globe, the PCS can be used to draw your property on a flat map.

In this class, we will be working with the Universal Transverse Mercator coordinate system (UTM) PCS. To minimize the errors in the projection, the UTM system is divided in different zones. Each zone is 6 degrees wide (longitudinal). Svalbard lies in the zone 33X. The coordinates are donated as:
514840.49 Easting
8683294.97 Northing
One full unit in this projection is the equivalent of 1 m, thus changes in position can be calculated easily. This video explains the concept and most important points.

Different projections are necessary as they fulfill different criteria. For example, Mercator projections display shapes and direction accurately, thus the shape of a country is correct and you can measure directions. Unfortunately, distances and sizes are not portrayed correctly. The Gall-Peters Projection on the other hand shows areas of equal size. The next table shows a map for each projection and a Mercator-map with true sizes.

Mercator Projection
(source)
Gall-Peters Projection
(source)
World Mercator projection with true country sizes and shapes (source)


For your convenience, the following table contains a lot more reading material from different sources. Two very good resources are the ArcGIS and QGIS help sites.
Datums, Projections and Coordinate Systems A brief summary and a few more concepts related to what we have done so far.
Datums ArcGIS Help.
Meridian Prime Meridian and Greenwich On Meridians.
What are geographic coordinate systems? ArcGIS Help.
Spheroids, spheres ArcGIS Help.


In session 2, we will start with the step-by-step guide to create a map.