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Using low-cost dual-frequency GNSS modules for cadastral mapping in Tanzania

Expert Contributions 2 Jun 2021 - 16:08 SAST

Using low-cost dual-frequency GNSS modules for cadastral mapping in Tanzania

Expert Contributions 2 Jun 2021 - 16:08 SAST

By William Perry Evans, Immaculata Mwanja and Digna Mushi

The complexities inherent in the current cadastral surveying system in Tanzania make it such that poor people can rarely, if ever, obtain proper land rights. By bringing communities together and using affordable dual-frequency receivers, we propose to change that.

On the Eastern coast of Tanzania lies Dar es Salaam, one of Africa’s fastest-growing urban centres. Experts project that it will achieve megacity status in the next decade, with ten million residents or more. Of this population it is estimated that 70% live in informal, unplanned settlements, subsisting on roughly a dollar per day.

What this means is that these millions of residents do not have access to their land or property rights, depriving them of social stability. To put it bluntly, “A property without a land title is worthless,” as Tanzania’s Housing Minister, William Lukuvi says. Obtaining a formal land title grants the owner access to credit, and provides essential protection to the urban poor.

Herein lies the challenge:​ ​How can Tanzanians living in informal settlements gain essential access to land tenure? This is just one piece of a much larger problem, as nearly a billion people worldwide live without legal title to their land. It is both a political as well as a technical challenge, where bureaucracy as well as precise surveying can be barriers.

To address the technical challenge, we propose the use of real-time kinematics (RTK) surveying with a newly released, low-cost, high-accuracy, dual-frequency sensor which runs open-source signal processing on mobile devices, to pave the way for land rights for the urban poor in Tanzania. This tech has recently become affordable to citizens, and can drastically reduce the cost to families paying for their land titles, making it up to a hundred times cheaper. 

Harnessing the power of this tech has been a local team of Tanzanian geographic information system (GIS) experts, who have conducted a pilot project in Dar es Salaam.

Understanding the context and cadastre processes

Cadastral surveys in Tanzania date back to the country’s colonial rule by Germany from 1890-1914, and then Britain from 1919-1961. Surveys served the colonial settlers by securing their land boundaries. Following independence, the primary objective was to provide geometric descriptions for equitable access to land and the registration of land rights.

Land parcels are the foundation of the cadastral survey system. In urban areas these are known as town plans. The three basic steps to conducting a cadastral survey in Tanzania are the request, execution, and submission. Taken together, these represent at least eight different procedures and a wait time of 67 days, according to the World Bank in 2018. Unsurprisingly, it lists Tanzania as the 146th most difficult country in the world to register property.

There have been different policies, strategies, and programs by the Tanzanian government to ensure all plots are surveyed and provided with title deeds. While the Minister of Lands reduced the cost of mapping each plot to 150 000 Tanzanian Shillings (±$65), it remains too high for the vast majority of informal residents who subsist on roughly a dollar per day. At the same time, professional surveyors cannot afford to go through the process and create the survey for any less. Other strategies include cost-sharing public housing programs and slums upgrading. But still these strategies could not address the scale of plot surveys needed, which is colossal and accelerating as informal settlements are expanding.

The complexities inherent in the current cadastral surveying system in Tanzania make it such that poor people can rarely, if ever, obtain proper land rights. The importance of cadastral surveys cannot be understated. By bringing communities together and using affordable dual-frequency receivers, we propose to change that.

A dual approach of tech and community

Our approach is twofold: on the one hand we are using the latest dual band RTK GNSS geospatial technology which is orders of magnitude cheaper than traditional equipment, and on the other hand we are encouraging whole communities to come together at once, reducing the time and cost of surveying to map their plots.

Engaging the community

Community cadastres are registers of the ownership and extent of property, generated by communities themselves. It is a combination of community mapping, with the official system of defining the dimensions and location of land parcels.

First we met with a former sub-ward leader in Makangira to find out whether the residents in Makangira wanted this project – they did.  We also met with the Chief Surveyor of Kinondoni Municipal Council, who informed us that we need to involve a registered survey firm to align with the Ministry of Lands’ legal requirements. He also advised us to meet with community members to educate them about the project.

To educate ourselves about the complexities of land registration, we met with the Landesa Tanzania office, launched in 2018 by the Minister of Lands. Their main goal is providing women with secure land rights, as evidence shows this increases income by 150%, reduces teen marriages, and increases school participation. This was such an important element to include that we invited one of their representatives to the community meeting in Makangira to explain the importance of women having land rights.

After patient waiting, we finally joined a large community meeting organised by the newly elected leader, where we introduced ourselves and the project. We listened to the community’s concerns, and explored the dimensions, pros and cons of doing the project. By the end of the meeting, the community confirmed they were ready to have their lands surveyed.

After this milestone, we hit several barriers. The invitation letter from one of the community leaders was delayed by a month. The District Executive Director in Kinondoni took another two months to provide us with the official permission letter to begin surveying. By March 2020, the Minister of Health had confirmed the first Covid-19 case, and we shifted to remote work.

We pressed ahead and decided to begin piloting the project in different communities, as Makangira’s was slow to respond. We visited three separate communities with ongoing regularisation projects to test our tools and processes, overcoming both technical as well as political hurdles along the way. 

In the end, we managed to survey 20 plots in the Segerea Ward, while simultaneously obtaining cadastral data from a professional survey company that had mapped the same plots before. This allowed us to demonstrate and assess the accuracy of the low-cost dual-frequency RTK receivers with open-source tools.

The technology

Professional surveyors use expensive real-time kinematics (RTK) equipment, which allow them to obtain highly accurate (centimetre-level) positioning in real time. A new sensor on the market allows users to establish affordable, centimetre-precision location. The Swiss company u-blox has released a dual frequency GPS sensor, along with a dual frequency antenna, for under $300. Tests done in August 2019 show an accuracy of 2 cm within Dar es Salaam.

We propose introducing it in a way that works hand-in-hand with communities as well as surveyors.

The RTK system (rover and base) works in combination with a simple Arduino microcontroller and local Android phones. It is not without challenges, but with the outputs achieved we believe it may empower Tanzanians and communities around the world who are living without land rights.

The team behind most of the fieldwork was OpenMap Development Tanzania (OMDTZ), a registered NGO operating across the country. OMDTZ has partnered with the Humanitarian OpenStreetMap Team over the years to conduct a variety of projects, from digitising building footprints to mapping drainage, soil sampling, flood extents, trash mapping, asset and threats, and doing flood responses.

The same tools and processes involved in this project have successfully been used in other OMDTZ projects before, for instance, creating a digital terrain model from aerial imagery and ground control points across the Msimbazi River. The expertise and evidence gathered in these other projects directly flows into this work.

Outputs and outcomes

In total, we mapped out 20 plots using the $300 u-blox ZED-F9P GNSS receiver, which shows the same degree of accuracy as $10 000 GPS receivers.

The best scientific evidence that we can present for the accuracy of this data comes from a method known as Precise Point Positioning (PPP) – a positioning technique that removes or models GNSS system errors to provide an extremely high level of position accuracy. It can deliver an accuracy up to 3 cm, and requires a longer period of time coverage to resolve local biases such as the atmospheric conditions, multipath environment and satellite geometry. This is the global gold standard.

While some of our comparative analysis is ongoing, the data shows clear evidence of accuracy, as verified by the Natural Resource Canada (NRCan), Canada’s government agency responsible for mapping and remote sensing. We have also created an online interactive map to interrogate the data and observe the differences up close: https://maphub.net/ImmaculateMwanja/gnss_plots 

There were additional benefits that arose from our work that are just as consequential as the outputs themselves. These include new partnerships and relationships with Landesa, Spatial Collective and Uhurulabs; a grant application for a drone project with Fondation Botnar; training for staff on the new equipment; and the production of open documentation for others to benefit from this knowledge and replicate our efforts in their own communities. 

Conclusion and lessons learned

We did not reach our goal of delivering title deeds to residents, which was the ultimate aim of this project, but now have strong, scientific evidence that our tools and methods can democratise land rights for poor people.

Our experience taught us several valuable lessons, about the technology, politics involved, and agonising bureaucracy of land tenure:

Technology can sometimes break down in the simplest of ways. We spent a full day in the field once, puzzled at why we could not get a fix on the satellites, only to realise later that the coaxial cable wiring of our equipment had a broken connection.

The community needs to lead the way. Land rights are so sensitive, and a key component of our approach is the idea that neighbours come together to reduce the time and cost of surveying, working together to agree on their boundaries. It also takes leadership from the authorities, and when this is in short supply surveying efforts fail.

The bureaucracy is just as bad as our research predicted. The fundamental barrier for informal settlements receiving their title deeds is no longer technological, it is political. Innovations such as ours must be parallel to legal and bureaucratic reforms.

None of this is to suggest that there is ​one ​way to go about the process of providing land rights to people, or even that the provision of title deeds is the only solution for insecurity of land tenure. It even occurred to us that ground surveying may not be the most effective means for accomplishing the ultimate goal of land rights for all. Fit-for-purpose land administration suggests other ways, such as using drones to capture high resolution aerial imagery and using this to digitise the cadastres with the help of communities and local leaders, as was done in Rwanda.

What we do claim is that we have found a viable, low-cost, highly-accurate solution for mapping properties, and we have no doubt that with political will community cadastres can change a billion lives.


This project formed part of an EthicalGEO initiative. Read the full report, including Natural Resources Canada’s PPP report generated from the fieldwork, here.

Editor’s note: If you enjoyed this article on democratising land surveying, you might also be interested to read “How dual-frequency satellite receivers will democratize land surveying”.