Data Collection And Data Entry
Data collection may be carried out in one operation together with the mapping exercise. This is especially true when a sketch-map is prepared, but may also be wise when a full-fledged mapping is done.
A so-called 'sketch-map' can actually be used as basis for an urban management GIS. This sketch-map should be reasonably true to scale. The sketch map will then be used to do the field survey. This will typically be measuring the size of the houses and plots fronting the road and the width of the road.
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The data collection will have to be set up in close cooperation with the municipality. Municipality staff should do surveys and (assist during) the subsequent data entry. Outside assistance may be needed in setting up the survey and during the start-up phase. The municipality will be willing to accept the data as accurate only when they are fully involved in data collection and data entry.
Clear and strict data entry procedures should be set up. Survey data will have to be filled in on prepared forms. Data entry should be passed through strict quality control where the data will be automatically checked for validity (e.g. low or high thresholds, choosing from a list of options, ensuring that required values are entered). Data entered from survey forms - and data changed - should be stored in a separate table. This table will be consolidated with the main table only after checking for data entry errors and duplicate entries, and vetting by the officer in charge.
Duration and frequency of surveys
Experience shows that the whole survey of some 30,000 properties in a city of about 250,000 took about six months with adequate staff. Taking into account that the procedures had to be worked out and adjusted during the survey (lessons learnt) it may be expected that a repeat in another municipality might take less time. On the other hand a new municipality will need time to get adjusted to this approach. A time frame of 6 months for the initial surveys seems reasonable.
The whole exercise can be viewed as a kind of municipal census. As long as procedures on registering new properties or changes in occupancy are not effective the exercise will have to be repeated regularly. For practical purposes a frequency of once every five years is recommended, as has been prescribed by the Municipal Act.
Data integrity
The value of a database (and a GIS is a database) is proportional to the accuracy of its data and the "coverage". Coverage means the percentage of the 'population' that is included in the database. If only 50% of the properties are included then the coverage is 50%. Coverage of 100% is probably not possible given the local context. To improve the coverage it is important to repeat the survey on a regular basis, and to check that all properties are included in the survey (quality control).
It is clear that data in a database should be accurate. However, the data resulting from the survey will always be a 'snapshot' in time representing the situation at a given moment.
Procedures to update the data should be devised and implemented but that may be difficult given the local setting. An example may be that a new owner or tenant should get proof of his registry with the municipality (and in the database) to avoid having to pay house tax for the previous owner or tenant, or to register water and electricity connections in his name. There should be a clear link between registration of changes and eligibility for municipal services. Again, this may be difficult to implement in the local context.
A completely different subject is database integrity. The database is the core, the heart of the whole system. It is very important that any changes made here are only made by authorised persons, and that such changes are checked for (data entry) errors, preferably by a second person. Any changes or additions to the database should only take place based on a paper record.
This record should be filed in a safe manner. Database integrity also means that there should only be one master database, on which all updates take place. Copies of the database should always be clearly marked as such! Users should take extreme care that changes intended for the master database are actually entered there, and not in a copy. For this reason the paper record for the change is essential! All the above is valid for any database in the system, be it a database like Access or a GIS. Changes in maps should also be made only after a verified and approved paper map with the intended change is presented, and subsequently filed in a proper manner. It is essential that regular backup copies are made of the master database.
