Map Revision
- The aim of revision is to keep maps up to date with changes taking place on the landscape- maintain their usefulness
- Revision of maps requires consideration of three factors:
- Revision policy
- The collection of information about changes
- The actual execution of these changes to the original material
Map Revision | 1. Revision policy
- The revision policy has to take into account the overall objective for the map seriesin terms of;
- its up-to-dateness
- the nature of changes
- the need to obtain information about changes
- the budget -the cost of issuing new sheets
Map Revision | 1. Revision policy
- Map revision techniques
- cyclic revision
- continuous revision
- selective revision
Map Revision Technique | a. Cyclic
- Revision in fixed periods
- Here, all the sheets are allowed to go unrevised over a number of years and then a specific operation would be mounted to renew them all
- Mapping agency collects information on changes during the intervening period using methods such as aerial photography
- Large scale map becomes out-of-date quickly, because they contain large amount of detail
- This method of revision is mainly applied to maps at smaller scales (1:10,000 and less)
Map Revision Technique | b. Selective
- This form of revision achieves revision of sheets in the series by an order of priority
- Priority being determined by urgency of demand or rate of change
- Special air photography is done
Map Revision Technique | c. Continuous
- This form of revision policy relies on a continuous inflow of data,- field survey
- This programme is normally employed for large-scale urban map series
- Nautical charts is the best example of continuous revision
Map Revision | 2. Revision information
- The collection of data on changes in the landscape can be a field survey, or study of new aerial photography etc.
- Data providers such as governments, individuals or private organizations;
- City Council may assist in continuous revision by supplying organizations with information about all new constructions in the city
- Private individuals who use topographic maps can inform organizations about changes or mistakes
Map Revision | 2. Revision information
- A common procedure for all types of revision is to keep a file copy of the latest issue of a map sheet and mark on it the changes that have occurred;
- These are normally colour coded to distinguish deletions from additions
- The changes may be marked directly on the printed copy, or on a registered overlay, and notes kept for this in a file
Map Revision | 3. Execution of revision
- Mapping agency employs varied system of reproduction to incorporate the new information into the existing map to reproduce new map;
- This depends on;
- nature of the original material
- completeness and correct fit
Map Revision | 3. Execution of revision
- The principal methods are deletion and addition;
- Additions new feature is to be added in an unoccupied area
- Deletions remove feature in an area
- Corrections that involve deleting the existing details and replacing with new information
Map Revision | Read on ...
- Research on the following areas of map revision used by mapping agency in Kenya;
- Propose an automation process {use flow diagram} to a mapping agency
That’s it!
Queries about this lesson, please send them to: jmwaura.uni@gmail.com
***References***
- Mapping, Society, and Technology, Steven Manson
- Web Cartography, Map Design for Interactive and Mobile Devices, Ian Muehlenhaus
- Web Cartography, Menno-Jan Kraak and Allan Brown, ITC
- Cartography, Thematic Map Design, Borden D. Dent
- GIS Cartography, A Guide to Effective Map Design, Gretchen N. Peterson
- Thematic Cartography and Geovisualization, Terry A. Slocum et.al
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