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ANNEXURE 1: QUALITY CONTROL METHODS

C LOGICAL AND PHYSICAL CONSISTENCY

Logical and physical consistency looks at whether spatial features are consistent when
it comes to topology, their extent, spatial relationship with other features, and geographic
location. You need to check the location of spatial features and their related attributes to see
whether they consistently and logically make sense. This can be done by:
 Producing thematic maps using variables associated with spatial features, including the
categorical and numeric fields.

 Randomly selecting between 20 and 30 points that can be identified in the study area to
check consistencies in the target population, government service point and road datasets.

 Queries of the spatial and attribute databases can also be done to see if the variable values
associated with spatial features are correct.

D REFERENTIAL INTEGRITY

You need to check how well attribute tables are able to link to spatial features and other tables. By
using a relational join (joining two tables together by matching values in fields that are common
to both tables) or geo-coding functions in GIS, you can easily determine the extent that attribute
tables are able to link to spatial features.

The spatial and attribute tables must have unique identifiers or primary and foreign keys to enable
them to link effectively. It is important to have a unique identifier to distinguish spatial
features from one another that may have the same geographic coordinates and to enable the
set of attributes associated with spatial features to be linked to them.

Consider the following:

❏ The target population dataset should have the unique enumeration area number if you are
using census enumeration area data.

❏ Service points should have a unique number that allows information from various divisions
in the department (e.g. finances, human resources, operations, beneficiaries, results) to
be linked to the spatial features. A good example of this is the Education Management
Information System (EMIS) number of the Department of Education.

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