Calculating area of rasters in QGIS

Posted by: Admire Nyakudya | 1 week, 4 days ago | Comments

QGIS raster functionality has come a long way and continues to improve. During my spare time, I am always on the lookout for interesting questions posed on

Speeding up multiple web map service requests using Python's asyncio and aiohttp

Posted by: Andre Theron | in Python | 1 month, 4 weeks ago | Comments

Geocontext is a Django app that retrieves information from multiple web based services for a specific query point. The services are arranged into hierarchies with multiple services in a group and multiple groups in a collection. It currently supports querying WMS, WFS & ArcREST services.

School GIS task: create a 5km COVID-19 lockdown exercise buffer around your house

Posted by: Gavin Fleming | in Education, QGIS | 3 months, 1 week ago | Comments

If you are doing some teaching in the classroom and some online and you are finding "blended teaching" overwhelming, this task is designed for asynchronous self study.

Does hosting your own server still make sense in 2020?

Posted by: Tim Sutton | 3 months, 1 week ago | Comments
Client: We need a server for this project and we want to host it in house
Me: Why?
The procurement of a server / multiple servers represents a large capital outlay. If you amortize that outlay over a 5 to 10-year lifespan, in my opinion, it is usually a poor investment. With cloud hosting, your equipment will be hosted in a facility with proper cooling, dust management, and power management - all critical for the long reliable operation of a server. Unless your project partners have facilities like this in place already, you can expect higher than average hardware failure rates and server downtime. In addition, a cloud provider has strong physical security, removing the possibility that equipment can be stolen or reappropriated.
If there is a failure on a cloud-hosted machine, they will have spare supplies on hand, or they can swap out the entire server in a short space of time, getting you back into production ASAP.
Additionally, if you invest capital in a server, the capacity of your storage and computing power is constant throughout the project. If you opt for cloud servers, you can scale up and down your infrastructure based on demand and usage patterns, saving financial and environmental costs.
Many cloud providers are now also running their data centers on green electricity (for example our preferred provider
Using a cloud server approach allows you to deploy your software using a ‘one server, one task’ approach where you deploy many small servers, each optimized for the workload needed. This removes the single point of failure outcome of deploying a single monolithic server and also prevents one wayward job on a server crippling all the other jobs on the server.
Cloud service providers also provide great failure support for things like nightly and ad-hoc server snapshots which image the whole server. The server can then be restored from that snapshot as a running instance. You can also create off-server and cross data-center backups.
For traffic management and network load cloud providers offer the ability to deploy into different regional data centers so that the traffic can be spread around the internet. Combined with using a content distribution network (CDN) like Cloud Flare, they can reduce the effects of latency introduced by far-away and heavily used sites.
The need for specialized staff to maintain servers is radically reduced when the server is cloud-hosted (in which case only a sysadmin or developer role is needed) versus on-site which will often also introduce the need for hardware technicians skills.
Lastly, I will mention that for most applications, the most common of which is a general-purpose web site, the argument that a server needs to be close-by for good performance is largely irrelevant since browsing web pages is generally not latency critical and a few milliseconds difference in response times will be unnoticed by users. In our company, almost all the servers we have deployed for African projects are located in Germany and the clients would be hard-pressed to notice the different response times wise.
There are a few critical things to consider when cloud hosting which may be used as arguments why cloud hosting is not suitable:
  • Some governments (e.g. Canada, Indonesia, others) have legislated that government datasets must be hosted on servers within the physical borders of the country. My response to this is usually to seek our local cloud providers. For example, Amazon has data centers in Canada that may be used for the Canadian govt. services.
  • The security requirements of the organization mandate that data may not leave the confines of the organization. In this case, the procurement of physical servers and hosting on-site may be a prerequisite. My comments about cooling, power supply, dust management, and physical security should be borne in mind then.
  • Cloud server costs can get away from you if not carefully managed. Some cloud vendors are, in my opinion, better suited for their ability to scale and bring online/offline computing resources than they are for hosting long-running servers. Amazon was an example of this last time I looked into it. Hetzner gives pretty good value, even for long-running servers.
  • Cloud servers may experience contention issues. In a project we have with a US-based client we were finding database performance very slow. It turned out that a lot of other servers using the same shared physical storage were adversely affecting disk performance.

Create a custom reference grid in qgis composer part 2

Posted by: Admire Nyakudya | in QGIS | 5 months, 4 weeks ago | Comments

This is a follow-up post on

Data defined settings for grid placements in QGIS 3.12

Posted by: Admire Nyakudya | 7 months ago | Comments

For a while now I have been trying to simulate the 1in50k topographic maps of South Africa. I started using QGIS since version 1.8 and I couldn't replicate the cartography on the topographic maps but over time as QGIS has matured, I could replicate the NGI maps. NGI uses proprietary software and then Adobe to fine-tune some context on the maps. For this exercise I used QGIS 3.12.0

Calculating intersects for map layers and map extent dynamically in QGIS

Posted by: Admire Nyakudya | in Python, QGIS | 7 months, 1 week ago | Comments

Recently we have been working on a project that involves simulating the 1 in 50k topographic maps in South Africa. Since we are using QGIS Server to print the map all the logic is set up in print composer. All  maps generated are dynamic (users can select a specific area within South Africa to print) and QGIS Server will use the map template to generate the map. 

The Longest River in the World

Posted by: Andre Kruger | in QGIS | 11 months, 2 weeks ago | Comments

Every now and then there might be a dispute about which is really the longest river in the world. As is shown in this National Geographic article. Even Wikipedia indicates that the fact that the Nile river is accepted as the longest river in the world as "disputed".

FOSS4G 2019 and QGIS in Bucharest

Posted by: Gavin Fleming | in Conference, FOSSGIS, GRASS GIS, GeoNode, GeoServer, Leaflet, PostGIS, Python, QGIS | 1 year ago | Comments

Open source GIS is alive and well and continues to grow in leaps and bounds around the world. Why so many Government entities in South Africa continue paying a fortune of tax-payers money for privative GIS and database software beats me, when wealthy, developed countries (as in most of Europe, for example) saw the light years ago and enthusiastically embrace FOSS.

Batch count vector features intersecting series of blocks in PostgreSQL

Posted by: Admire Nyakudya | in Database | 1 year, 3 months ago | Comments

The national mapping agency in South Africa (NGI ) caters for national mapping, digital topographic and other Geo-Spatial Information services. The department is mandated to provide spatial data for the whole country. In most cases, they have an in-house team that is responsible for digitizing aerial photography, field validation to produce vector data that is used to make 1:50 000 topographic maps.

Show only features within current Atlas feature - QGIS 3

Posted by: Admire Nyakudya | in QGIS | 1 year, 4 months ago | Comments

In our endless endeavour to spread QGIS, I was invited to conduct QGIS training at the Surveyor General Department in Swaziland.

Creating a live, topic specific mirror of OpenStreetMap in PostGIS

Posted by: Tim Sutton | in Docker, PostGIS, QGIS | 1 year, 5 months ago | Comments


In this article, we will do a walk-through of creating a live mirror of OSM for a specific country or region and for a specific set of OSM features. For this example, we will fetch all building data for Angola into a PostGIS database, and update that database with new features as they arrive in OSM. Providing an OSM mirror in this way is a powerful tool to pair the power of OSM with the power of QGIS and PostGIS. Now you will be able to do offline analysis of the data in OSM. How does this all work? Here is a little diagram that illustrates the underlying architecture (click for a larger version):

FBIS 2 Launch Workshop

Posted by: Tim Sutton | 1 year, 5 months ago | Comments

Mounting a storage drive in Hetzner cloud for rancher deployments

Posted by: Admire Nyakudya | 1 year, 5 months ago | Comments

This article builds upon an earlier blog post by Tim Sutton on using-a-sambacifs-mount-as-a-docker-volume. In the previous article, Tim described the process of mounting a storage driver in detail.

How to make beautiful lollipop call out labels in QGIS

Posted by: Tim Sutton | in QGIS | 1 year, 5 months ago | Comments

Call out labels are a handy cartographic instrument for attaching labels to features on the map where you want the label to be offset from the feature being labelled. It allows you to prevent the map becoming overcrowded. I call the variant I describe here 'lollipop' labels because the 'callout line' is rendered with a decorative ball at the end.

Using NOTIFY to automatically refresh layers in QGIS

Posted by: Tim Sutton | in PostGIS, QGIS | 1 year, 5 months ago | Comments

One of the most brilliant but little-known features of QGIS is the ability to trigger layer refreshes and events in response to notifications from PostgreSQL. This was developed by the wizards from Oslandia and is easily added to any existing table in your PostgreSQL database - including PostGIS tables. This feature was added in version 3.0 (see Take for example this simple table:

How to easily add South African and Namibian toposheets as XYZ tiles to QGIS

Posted by: Tim Sutton | in QGIS | 1 year, 8 months ago | Comments

Thanks to the great work of Grant Slater and the OpenStreetmap team, there are freely available XYZ tilesets for South Africa and Namibia 1:50 000 series toposheets which can easily be added to QGIS. Here is the general procedure to add a layer:

Year in Review: 2018

Posted by: Carina Christelis | 1 year, 9 months ago | Comments

It’s been another awesome year for our Team. We have come a long way since establishing Kartoza in 2014, building many different software products, making friends and working with existing and new clients. Forming a company around an open source friendly business model presents many challenges but is also extremely rewarding. Here is our 2018 year end review that we would like to share with you! 

Adding elevation to a line from a DEM in PostGIS and maintaining accurate measures

Posted by: Gavin Fleming | in PostGIS, QGIS | 2 years, 1 month ago | Comments

This is the second in a three part series on the behind-the-scenes GIS work that can go into planning a complex event, in this case the Cape Town Marathon.

How to create a point distance marker layer along a line in PostGIS

Posted by: Gavin Fleming | in GRASS GIS, PostGIS, QGIS | 2 years, 1 month ago | Comments

This is part 1 of a 3-part series.

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