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, 20-23 March 2017

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

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

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

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

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

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

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 0.5 m Regular urban 2.5m Rural (excluding protected areas) 2.5 m

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

Training in the GIS Lab

Commissioner of Statistics Inspecting the Work

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

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

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

Images Before Mapping

Images after Mapping

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-2016- Aug 2016 July-2016-June 2017

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