Basic spatial unit frame developed to spatially harmonise datasets

July 13th, 2019, Published in Articles: EE Publishers, Articles: PositionIT, Featured: PositionIT

The development of the Basic Spatial Unit (BSU) frame, the grid shown in the map below, is a first step in shedding new light on the complexity of the South African landscape and seascape.

A technical team from Stats SA, the South African National Biodiversity Institute (SANBI), and the National Geo-spatial Information (NGI) component of the Department of Rural Development and Land Reform (DRDLR), recently developed the BSU frame as a way to begin spatially harmonising different datasets. The project was initiated as part of the System of Environmental-Economic Accounting (SEEA), an international framework that measures interrelationships between the economy and the environment [1].

BSU frame covering the Cape Town harbour and surrounds.

The map above, covering the Cape Town harbour and surrounds, shows what the grid looks like. Every cell in the BSU frame is exactly the same size, measuring 100 m by 100 m (or 1 ha). Spanning the entire country, the layer consists of 728-million cells. The Prince Edward Islands and South Africa’s exclusive economic zones in the marine environment are also covered, as well as the river drainage basins shared with neighbouring countries to the north.

The technical team have already begun experimenting. By analysing available satellite data using the BSU grid, the team have been able to assign one of three broad land-use types (natural and semi-natural vegetation, cultivated areas and built-up areas) to every cell. Data from 1990 and 2014 have been used, allowing the team to identify those cells that have experienced a change in land use over time.

This is the first step on a much longer road. Eventually, other datasets will be “snapped” to the BSU grid. The population census, for example, provides a wealth of data on demographics, employment, income, housing and services – often at street-block level. Data are available for the years 1996, 2001 and 2011, with the next census planned for 2021. By incorporating census data, researchers will be able to start examining possible interrelationships between people and the natural environment.

In time, economic datasets might also be included. This will allow for evaluations such as determining whether a new large mine operating in a particular cell eventually correlates with a rise in income and employment in surrounding cells or impact on water quality.

The BSU grid forms the foundation on which large, location-rich data can be spatially harmonised, allowing analysts and policymakers to make meaningful comparisons across datasets and over time.

References

[1] United Nations, What is the SEEA? Available online: https://seea.un.org/

Contact Stats SA, info@statssa.gov.za

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