A picture is worth (more than) 1000 words

By Levi Westerveld

By GRID-Arendal

June 18^th, 2016

The Limpopo River rises in central southern Africa and stretches through Botswana, South Africa, and Zimbabwe before meeting the Indian Ocean in Mozambique. Environmental experts from these four countries met recently in Harare to learn how to use maps and satellite imagery to tell compelling stories of environmental change in the basin.

Bringing Visual Knowledge to the Limpopo River Basin Atlas Workshop.

The Limpopo basin is prone to regular droughts and floods causing the upstream countries to hold back water stored in dams during droughts, and in the process creating shortages in the downstream regions. When water is in abundance the same upstream countries are forced to protect their dam infrastructure by releasing water and causing floods downstream.

To guide policies and decisions in order to balance upstream and downstream needs, all the riparian countries in the region signed the Limpopo Watercourse Commission (LIMCOM Agreement) in 2003, currently overseen by an interim commission. Information is critical to planning and decision-making. This need for scientifically credible and evidence-based approaches to planning led LIMCOM to commission an atlas of the changing environment of the Limpopo.

Facilitators and participants from Zimbabwe, Mozambique, South Africa, and Botswana at the workshop in Harare, Zimbabwe, June 2016.

A training workshop organized by GRID-Arendal in June 2016, and hosted in Harare by the Southern Africa Research and Documentation Centre, was designed to help regional experts prepare visual material for the atlas, including maps, graphics and satellite images.

By combining text with visuals the Atlas will provide policy makers with up-to-date information on the current landscape of the Limpopo River Basin. This will help them to develop stronger policies and pursue transnational collaboration for better management of the regional environment.

The workshop was hosted by the Southern African Research and Documentation Center (SARDC) in Harare.

During the workshop, participants also learned how to use satellite imagery to show how the landscape has changed over a specific period of time. These images are called “change pairs.” Large scale human activity such as the construction of dams, deforestation, or natural events such as floods or wild fires can be shown when comparing satellite imagery. These images are then backed by research and expert knowledge which explain the source and impact of observed changes.

Danai Matowanyika works in Zimbabwe and is helping to develop the atlas. He participated in the workshop and says it “introduced many practical applications that can be used to improve this atlas. The skills can also be applied in various initiatives across the region.”

“The training is very relevant for my teaching and research career in the field of land agriculture, particularly soil resources,” said Felicidade Jorge, another atlas author from Mozambique. “With the knowledge acquired I feel that I have secure basis to discuss quality related results with colleagues from the GIS area.”

Creating a map (the more technical part)

What does it take to create a compelling map? Quite a lot of work! Below we illustrate with images some of the steps learned by participants to create a simple basemap of the Limpopo River basin. A basemap is the background of a map. It shows the bare landscape of a region on top of which the location of roads, towns, political boundaries, dams, power lines and other data can be superimposed to tell a compelling story.

You can think of cartography a bit like making a salad. You have to find the right ingredients, mix them, and finally combine them in an interesting way. For a basemap, all it takes are two primary products from which derivatives are produced: (1) An image that shows changes in elevation in the area of interest (called a Digital Elevation Model or DEM) and (2) a satellite image of the same area.

Step 1 – From the elevation image, we can use computer software to create two other images. One uses the elevation data to create an image showing the relief of the terrain, highlighting mountainous regions. This is called a “hillshade”. The other assigns different colors to specific elevation ranges and is called a “hypsometric” tint. In that image, lower elevation regions are shown in green. Areas with a higher elevation are shown in beige, brown, and grey.

Step 2 – The hillshade and hypsometric tint are combined to create an initial version of the basemap. To combine them, the two images are simply superposed. The top layer is transparent so you can see the layer underneath.

The initial basemap combining the hillshade and the hypsometric tint.

Step 3 – Then we extract vegetation information from the satellite image, as well as ground and water information to create three new images showing each of these elements as illustrated below.

Write your story here. (Optional)

Step 4 - We integrate these three images with the first version of our basemap to create a more detailed version that can be used as the basis for our map creation.