You will need to make a decision over the type of data model you wish to use – Raster or Vector – and it is important to realize that a particular data model may be better suited to your application. However, the choice of data structure you can use for any particular application is often an arbitrary decision, since GIS software will generally support one particular model as fully as another.
Data structure is a logical arrangement of your data in a format suitable for you and your system to manage it. Whichever model and structure you choose, you will, of course, need to convert the data you already have into a format which can be used by the GIS. Converting data into digital format is a labour intensive activity, and can account for up to 80% of the total system cost. Therefore, time spent on fact-finding and planning is time well spent.
Central to any data capture plan is a thorough internal data audit. This will help you determine the size, scope, and cost of the task ahead. Given that few organizations are able to redeploy staff to tackle a data capture exercise, two realistic alternatives remain. Either you can hire, train, and equip a dedicated team, or you contract the job to a specialist bureau. The latter will almost certainly be able to undercut the in-house option, but you need to ascertain that this will not be at the expense of quality control and flexibility. Data capture can also be an opportunity to improve the quality of your data by incorporating new information with the old.
You also have a choice to make between methods of converting your data: scanning and vectorisation. Scanning offers ease and speed, but the resulting raster images lack the intelligence needed for vector-based GIS. A fair degree of operator expertise is also required, and compression techniques (typically run-length encoding) will need to be applied to keep the files to a manageable size. Vectorisation can be applied automatically or interactively to produce intelligent vector files. Table digitizing has the advantage of employing inexpensive digitizing equipment. However, operator training is needed to obtain good results, especially from indifferent originals. Conversely, the procedure is laborious, time-consuming and, hence, costly. Other possibilities such as raster-to-vector conversion and pattern recognition are worth considering in this trade-off between productivity, cost, quality, and usability. While scanning and table digitizing will accommodate the bulk of conversion needs, from text documents to line art and even video images, special techniques have been developed to enter material from other sources. These range from simple programs that facilitate the keyboard entry of survey co- ordinates to techniques that reconcile aerial photographs with base maps. Photogrammetric, remotely-sensed and CAD-generated data represent yet further potential input sources.
For more information on GIS systems or the data conversion methods, please contact us.