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Emerging Census Technology – GIS & GPS

Enumeration Areas & Enumerators

Many countries will be using some element of Geographical Information Systems (GIS) during the 2010 round of census.  Typically GIS software is used with a combination of high-resolution satellite imagery to confirm and define administrative boundaries.  These boundaries are used to determine the enumeration areas (EAs).  In previous rounds of census such mapping has been undertaken using paper-based maps.

For face-to-face census data collection an enumeration area is typically allocated to an individual called an enumerator, who visits each residential structure and collects the census data during the census period.  Enumerators and are commonly temporary staff, employed in large numbers.  The number of residential buildings varies for each enumeration area and so does its physical size depending on a number of variables, policies and procedures within each National Statistical Office (NSO).

GIS & GPS

To prepare for Censuses using GIS software, field exercises are undertaken to collect latitude and longitude waypoints from Global Positioning System (GPS) devices.  This allows for certain landmarks and other key features to be identified and referenced within the GIS software and the mapping process.

Some countries have collected GPS points for the corners of each enumeration area.  Other countries capture GPS points for each residential building.  The collection of GPS data is a significant overhead but it is widely agreed that, once the GPS data has been captured, the use of GIS software offers a significant reduction to the cost and time needed for the census data collection.

There are four main scenarios: 1) traditional enumeration area data collection, 2) GPS house listing and enumerator area data collection, 3) PDAs with GPS for enumerator area data collection and 4) simple GPS devices and enumerator area data collection.

Scenario 1: traditional enumerator area data collection (paper based)

In preparation for the census, GIS software is implemented in an NSO, enumeration area boundaries are defined and checked in the field.  During the Census period, enumerators collect census data for the residential buildings within their EA. Enumerators are supplied with maps and satellite images to help with their collection activity.

Enumerators may have to manually record the building number of each residential structure visited so that the census database holds information relating to each structure.  However, the building numbers cannot be easily cross-referenced within the GIS software as there will not be GPS points for each building.     

Scenario 2: GPS house listing and enumerator area data collection (paper based)

A small number of countries have identified the need to associate the census data with a known GPS reading for each structure.  The GIS software can then be updated with the census data and so be used for planning, emergencies, tracking population trends and thematic mapping.

To achieve this, most countries have undertaken a pre-census house-listing exercise, using field workers with hand-held GPS devices, unique number plates/plaques and EA maps.  Each residential structure within an EA is visited and a GPS reading is taken.  The reading is allocated a unique number and that number is given to the householder in the form of a plate/plaque for them to display on the structure at the point of the census.  During the census the enumerator records the plate/plaque number on the census form (assuming paper-based data collection), thus allowing cross-referencing of the GPS locations with the census data.

House-listing exercises can be undertaken over a much longer period of time before the census, so the number of temporary staff required for them is less than needed for the main census exercise.  There can however be duplication if, for example the home owner is not present during the house listing visit and repeat visits are needed.

Scenario 3: PDA/pocket PCs with GPS for enumerator area data collection (digital)

In this scenario, census data and GPS positions are collected together at the point of census enumeration with the aid of a Personal Digital Assistant (PDA) with the capability of both recording GPS points and capturing census data.  Each enumerator needs a PDA, which can be pre-loaded with EA Maps.

There are however significant technical, financial and logistical issues for countries which choose this scenario, including: 

  • relatively high costs of PDAs with GPS functionality  
  • creation and loading of data onto the PDAs
  • IT skill level of enumerators and within the NSO
  • risk of failure of the PDA in the field
  • security of the data and of the PDA device itself
  • battery charging and life

Some regions are considering a PDA share scheme amongst neighbouring countries to spread the cost of the initial purchase of large numbers of PDA devices.

If a country has ‘honest’ enumerators, suitable IT skills and the finance to procure large numbers of PDA devices, then this is an attractive option for census data collection with GPS reference points.

Scenario 4: simple GPS devices and enumerator area data collection (paper based)

In this scenario the enumerator carries a simple GPS device that displays latitude and longitude data for each residential structure.  The enumerator writes the latitude and longitude information onto the census form during the census data collection.  This means that the physical record of the census data for every residential structure will have a GPS point associated with it.  Using form scanning techniques such as Key From Image (KFI) and Intelligent Character Recognition (ICR) in the data capture process, all census and GPS point data can be imported into GIS software.

The DRS Cense GPS device can be attached to an enumerators clip board, or simply be carried using a lanyard around the neck.  It only has an on/off button, uses readily available batteries and holds no data.  Nor does it require any infrastructure to produce results as it works by tracking signals from existing satellites.

Some of the benefits of this scenario include: 

  • helps deter fraudulent enumeration, as a specific latitude/longitude point is required
  • helps enumerators confirm that they are at the start location on their EA map
  • a single collection exercise is required
  • no IT skills are required for operation or setup
  • significant cost saving over more expensive PDA devices 

This scenario an attractive option for countries who wish to contain costs, avoid pre-census field work or who have limited IT literacy.