I recently had a great opportunity to produce a map for a dive operator called Oceanfjord, located near Ålesund in Norway. They had a company called Longvas Oppmåling perform a very detailed measurement of the sea floor in a potential dive location and it was my job to produce an easily understood and good looking map for potential clients. A map that clearly shows the sea floor surface (aka bathymetry) as a grid or “isarithmic map” and elevation contours and a good base map for orientation.
This was my first gig as a freelancer, so I needed to set up a working environment on my computer. Furthermore, it’s been a while since I last worked with elevation data – I was thrilled to get started!
The client gave me a bunch of files and a few directions as to what they wanted and I dove in to it.
I used to work for a big consultancy company called Grontmij where the work stations were Windows and we had a big infrastructure and lots of licensed software. Since I stopped working there, I started working with only Linux work stations which meant that I was going to solve this task on a new platform. I went ahead and installed the awesome open source GIS software called QGIS. I now had a bunch of files in DWG, DXF and XYZ format. I was not familiar with DWG/DXF files from before, but QGIS was fully able to open and show the DXF file containing depth contours at 2 m intervals with an attribute table. It was also able to open the XYZ text file with raw data in the form of nearly two million measure points.
The data didn’t contain information about map projection, nor did the contour attribute table contain any numeric values for the depth. Furthermore, I had no grid – just contours and loads of measure points in a huge XYZ file of over 115MB. I had the following challenges ahead of me:
- Find correct Spatial Reference System (SRS)
- Create a grid and an isarithmic map
- Classify and colour the contours
- Get a good background map
- Fine tune the cartography and map layout.
Read the following pages for details on how I solved those tasks.