1. CENSUS MAPPING USING SATELLITE IMAGERY IN MALAWI
Presented by
Isaac Chirwa, National Statistical Office
Zomba, Malawi
at the United Nations Regional Workshop on the 2020 World Programme on Population and Housing Censuses: International Standards and Contemporary Technologies
Lusaka, Zambia, March 2017

2. Introduction
Population and Housing Censuses (PHCs) have regularly been conducted in Malawi since the colonial era
However, the most comprehensive censuses have only been undertaken during the post-colonial period starting with the 1966 census and every ten years thereafter.
A vital component of census work is the delineation of statistical areas referred to as Enumeration Areas (EAs) for field enumeration, which is the spatial foundation for census datasets
Thus every census undertaking in Malawi starts with mapping

3. Traditional Authority (300)
Census Mapping
The administrative structure of Malawi which is adopted by NSO is shown in this figure
The national boundaries and in most cases the districts boundaries do not change
Hence the first step in mapping that NSO undertakes starts with updating of TA boundaries (new) followed by a complete re- mapping of EA boundaries
Region (3)
District (32)
Traditional Authority (300)
Enumeration Area (13,000)
Village

4. 2008 Census Mapping Methodology
The 2008 Census Mapping was manual based involving canvassing of the whole length and width of the country in order to demarcate it into the small EAs
Hand held GPSs were the most important tool used by the mappers to collect points used to map the EAs
However, this methodology was not only prone to mistakes, it was also very tedious and long
In the 2008 census mapping, the process took 4 years and had to be hurried when it was observed that the exercise will not finish before the census starts

5. 2018 Census Mapping
The 2018 Census Mapping started with drafting of the census mapping strategy
It outlines the objectives, outputs, organizational structure, technological choices, methodology, capacity building requirements, timelines and budget
The document was used as a blue print for the census mapping exercise and was very instrumental for resource mobilization especially from the government who were the main financiers of the mapping exercise.
The total budget for the 2018 Census Mapping was US$1.6 million

6. Software and Hardware
There were very few GPSs, computers, UPSs and other hardware equipment available for the census mapping by the time the strategy was developed
It was thus planned that 15 GPSs, 25 computers, 10 laptops, 25 notebook computers, 4 UPSs, 2 plotters, a server and 15 printers be bought to support the census mapping activities
On the software side, NSO decided to buy ArcGIS v 10 licences
With funding from the government all the hardware and software have been procured

7. Census Mapping Methodology
Due to the shortfalls experienced by NSO in the census mapping exercise in 2008, NSO decided to use satellite imagery as the main tool for 2018 census mapping. NSO also decided to use CAPI for the main census thereby abandoning the use of pen, paper and scanning
Census Enumeration
EA Demarcation
Satellite Acquisition
Planning

8. Satellite Imagery
NSO recruited Regional Centre for Mapping of Resources for Development (RCMRD) from Nairobi Kenya to provide the satellite imagery and the Technical Assistance required to do the mapping
RCMRD provided satellite imagery of the following resolutions
Ultra-urban m
Regular urban m
Rural (excluding protected areas) m

9. Training and Pilot
Once at NSO, RCMRD went straight to train a pool of 20 mappers from NSO
The officers were trained on how to capture dwelling frame (DF) and demarcate the EA boundaries using Arch GIS software
Piloting of the tool was done in four districts to test the new tool
Once we became confident that it is working, it was rolled out to the rst of the country
All the demarcation is being done in the GIS lab, field work only involves verification

10. Training in the GIS Lab

11. Commissioner of Statistics Inspecting the Work

12. Modus Operandi
The plan is to have between 200 and 300 households per EA
Structures are used as proxy for households
The mappers use dots by clicking on each and every structure that is deemed to be a household
Once the structure has been clicked it is marked red, counted and coordinate points registered automatically
Using features, such as rivers, roads e.t.c, the mapper draws the boundary keeping in mind that an EA should have between 200 and 300 households

13. Modus Operandi…..
The small number of households per EA will enable the enumerator collect information from all households within the specifies short census period
However, number of EAs will drastically. The current estimate is that they will reach 25,000 from 13,000 in 2008
This has budgetary implications as it means recruiting more enumerators, procuring more tablets and other costs

14. Field Verification
After mapping in the lab, the mappers take the maps to the field to do field verification
They carry with them hand held GPSs which they use to verify the boundaries drawn in the lab
The exercise is also used to verify if the marked structures are indeed households
Back to office, the results are compared to what was drawn
Any deviations are rectified and corrected

15. Images Before Mapping

16. Images after Mapping

17. Work plan and Timeline Dec-2015- Jun 2016 Mar-2016- Aug 2016
Planning
Acquisition
EA Demarcation
Draft strategy
Hire
consultant
Equipment, Technology
Other data
Human resource
Satellite Imagery
DF generation
EA demarcation
EA map production
DF field verification
DF updating
Mar Aug 2016
July-2016-June 2017

18. Advantages and Disadvantages of Satellite Imagery
Mapping using satellite Imagery is fast and less tedious. While the 2008 census mapping took 4 years to complete, the 2018 census mapping will take less 1 year
Boundaries using satellite imagery are more accurate as the mapper sees where feature are physically located. There were many instances where the 2008 maps when superimposed on the satellite imagery showed that they were completely off the feature they were following
Since the main census will be conducted using CAPI (which has a GPS provision), it is easy to monitor that each household has been visited by the enumerator
However, satellite imagery is very expensive. RCMRD alone charged NSO US$1.1 million for the images and technical assistance. Same thing with CAPI for the main census is going to cost an additional US$10 million