Data visualization using desktop GIS tools

• QGIS: visualizing coral reefs and Millepora
  • Installation
  • Data sources
  • Adding the base map
  • Adding the coral reef layer
  • Adding the OBIS occurrences

QGIS: visualizing coral reefs and Millepora

In this demo I will show how to combine OBIS data with spatial data from other sources in the desktop GIS application QGIS. All required files, except the coral reef layer, can be found here.

Installation

QGIS is available for download https://www.qgis.org/en/site/forusers/download.html.

Data sources

We’ll use three data sources to generate our map:

• Any CartoDB basemap.
• OBIS occurrences of the genus Millepora. Download the dataset as CSV using the OBIS mapper.
• The Global Distribution of Coral Reefs dataset compiled by the UNEP World Conservation Monitoring Centre (UNEP-WCMC). You will need to fill out a form before you can download the dataset.

Adding the base map

We’ll use a tile layer from CartoDB as our base map. To be able to do this, we need to install the TileLayer Plugin:

Plugin installation

Creating the layer definition

Create a file named cartodb.tsv (Tabbed Separated Values) containing this line:

CartoDB	CartoDB	http://a.basemaps.cartocdn.com/light_all/{z}/{x}/{y}.png

Adding the layer

Now open the plugin, go to Settings and select the directory where you stored the layer definition file.

You should now be able to add the CartoDB base layer:

Adding the coral reef layer

To add the coral reef shapefile, first extract the zip file you downloaded earlier (WCMC-008-CoralReefs2010-ver1-3.zip). Then go to Layer > Add Layer > Add Vector Layer, and select WCMC-008-CoralReefs2010-ver1-3.shp. Adjust the styling of the coral reef layer by clicking the colored square in the layers panel. Here I chose a bright red fill and no line:

Adding the OBIS occurrences

To add the Millepora occurrences, go to Layer > Add Layer > Add Delimited Text Layer. Select the CSV file and click OK. The CRS selector window will now pop up. Make sure that EPSG:4326 is selected, because we are adding points with coordinates in decimal degrees to a map that uses the Web Mercator projection (EPSG 3857).

To change the symbols, click the symbol next to the layer you just created, go to Style, select Categorized, select the column you wish to use for coloring the symbols (tname for example), and click Classify. Play around with the marker settings.