Digitizing is the process by which coordinates from a map, image, or other sources of data are converted into a digital format in a GIS. This process becomes necessary when available data is gathered in formats that cannot be immediately integrated with other GIS data.
The Digitizing Process
- Manual Digitizing
- In this method, the digitizer uses a digitizing tablet (also known as a digitizer, graphics tablet, or touch tablet) to trace the points, lines and polygons of a hard-copy map. This is done using a special magnetic pen, or stylus, that feeds information into a computer to create an identical, digital map. Some tablets use a mouse-like tool, called a puck, instead of a stylus. The puck has a small window with cross-hairs which allows for greater precision and pinpointing map features.
- Manual Digitizing is still a useful technique because of its ability to accurately copy maps in poor condition. Computers have a higher risk of error when interpreting information contained on a faded, stained, or poor quality map or image. Manual Digitization is limited by the visual acuity and accuracy of the digitizer. The process ,also, is more time consuming than Heads-up digitizing.
- Heads-up Digitizing
- This method involves scanning a map or image into a computer. The digitizer then traces the points, lines and polygons using digitizing software. This method of digitizing has been named "heads-up" digitizing because the focus of the user is up on the screen, rather than down on a digitizing tablet.
- It has largely replaced Manual digitizing because of its speed and accuracy. It is, however, limited to using scans of high quality maps and images. Since the tracing is done on a computer, lines can be set to snap together and polygons can be programmed to share an edge thus removing accidental sliver polygons. Heads-up digitizing also reduces or removes the need for digitizing tables.
- Digitizing tips
- Search for the digitized data first. Digitizing is very time consuming and often the data is already digitized.
- Use multiple geographic sources when digitizing. Referencing such sources as scanned topographical maps, orthophotos, remotely sensed data, and in situ data will increase the accuracy of the digitized data.
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