Disaster Risk Reduction, Mapping

Counting the Population is as Easy as 1, 2, 3 with the Help of GIS


My three year old is fascinated with counting. Probably one of the most memorable instances of her enthrallment was her sounding off “1, 2, 3, 4” as a family of sisters occupied the bench directly behind us in church. “Four, Mommy, Four!” she shouted as she also pointed it out on her fingers. Seen from my toddlers enthusiasm, there is an innate nature in all of us to know “how many?”.

Conducted on average, every 10 years, the purpose of a census is to gather information about a population’s housing conditions, demographics, social and economic characteristics. It includes collecting data like age, gender, education and employment. It helps us to answer questions like: how many children in your country have completed secondary education? Or how many 20-year olds who live in a particular area and are unemployed? Or how many people in total live on your island? Basic information, such as these, are important for the purposes of planning, development and the improvement in the quality of life for a territory’s citizens.

Counting the population of any country, regardless of the size, can be seen as a daunting task. Geographic Information Systems (GIS), provides a platform, however, to enable data collectors to be more efficient in locating buildings and ensuring that this intimidating work is made a lot more manageable.

In its last count of the population, the Montserrat Statistics department enlisted the use of GIS in the Montserrat 2011 Population and Housing Census to ensure that the enumeration data collected was as accurate as possible. Some visual representations of the data were produced, such as the map below which shows the usual resident population of 4,922 based on gender (male and female) and region (northern, central and southern).

Source: http://www.gov.ms/wp-content/uploads/2011/02/Montserrat-At-A-Glance.pdf

The leader* and the team from the statistics department had a clear vision of how the country should be divided in terms of Enumeration Districts and Areas. Some areas were demarcated using naturally occurring features on the landscape, such as ghauts and mountains, and others were demarcated using man-made features like roads. A total of thirty-six enumeration areas were created and detailed maps were prepared for each area. This allowed the areas to be divided into manageable sections and allowed the data collector, with training in map reading, to be more efficient in canvassing the area. The demarcated enumeration areas now provide a base for the collection of additional data and allows for easy comparison and correlation of datasets in preparation for the 2020 round of censi.

The Montserrat 2011 Population and Housing Census benefited from imagery, which was recently collected in 2010 (see my previous blog at https://wp.me/pa7Lux-7o).  The one-year time difference was considered negligible, allowing for a certain level of confindence in the accuracy of the maps, which were produced. Any missing building footprints were drawn on the map while the area was being canvassed, and then later updated. For any future census activity, access to current imagery will play a huge role in its success. Current imagery can be analysed using tools in GIS which will help to determine changes since the last count. One special way of determining change is to use image classification techniques and compare with previous imagery. Utilising this method, new buildings footprints can be identified and quickly extracted using GIS tools and models.

Furthermore, a census provides data, which is critical for disaster risk reduction. Knowing the spatial distribution of the population and its demographic details is key in increasing a Government’s ability to take appropriate action and reduce the loss of human life. Population density maps provide an outlook to assess risk before and the quantification of a population affected after any disaster.

*This post pays tribute to the late Mrs. Katrina Ryan who was the head of the Statistics Department at the time of the Montserrat 2011 Population and Housing Census in Montserrat. She had an endearing passion for the accuracy of statistical data. May her soul rest in eternal peace.

Lavern Rogers-Ryan is a geospatial consultant specialising in disaster risk management and recovery. She is currently head of the GIS Centre within the Government of Montserrat. Learn more about geospatial services in disasters at www.lavernrogersryan.com.