Cleansing
For consistency and quality, It's important that your GIS information is correct. Data cleansing can help with this and is often applied during the Migration or Capture stages of a GIS project. Data Cleansing can be applied for example to ensure that a data item conforms to a set list of allowable values for that data by mapping from a value in the original GIS to a new value in a new system. For example a value of 'dock' might have been acceptable in the original system but it must be mapped to 'harbour' or 'port' in the new system. In this the data cleansing may have to take account of other factors such as the usage of the 'dock' - a usage of 'container' may suggest a port whereas a usage of 'pleasure' may suggest a harbour.
Validation
Data validation is related to cleansing in that a cleansed value should always be valid. Validation checks can be broader however and can be used to give a measure of the overall data quality in a GIS (or any data set). Thresholds for quality may be set, for example - again in a migration project - acceptance criteria may state that the type for a particular object need only be present for 95% of all objects migrated.
Validation checks can be applied to various aspects of the data held in a GIS be that topology, connectivity, position or attribute information.
