In GIS, Digitizing is the process of tracing features to turn geographic data from a hard copy or scanned image into vector data.
Features from the traced map or image are captured as coordinates in point, line, or polygon format during the digitizing process.
The process of turning geographic features on a paper map into digital format is known as digitizing. The spatial data is made up of the x, y coordinates of point, line, and polygon characteristics. During the digitization process, the feature properties are also recorded.
It’s the most frequent and time-consuming way to make a spatial database. When existing maps are accessible as a data source, this method is particularly useful. Using a digitizer table and cursor, coordinates of point features, line features, and polygon features are manually pointing or tracing.
The device correctly measures the cursor position in order to generate coordinate data in digital form. Despite the fact that scanning has largely replaced digitization, digitizing tablets are still used to turn existing maps and drawings into GIS.
Types of Digitizing
there are number of digitizing methods. Manual digitization entails using a puck to trace geographic features from an external digitizing tablet (a type of mouse specialized for tracing and capturing geographic features from the tablet).
The method of tracing geographic features from another data set usually an aerial, satellite image, or scanned image of a map directly on the computer screen is known as heads up digitizing (also known as on-screen digitizing).
Automated digitization entails creating vectors with image processing software that includes pattern recognition technologies.
A. Manual Digitizing
Manual A digitizing tablet is used to digitize. The digitizer traces all of the lines from the hardcopy map like Toposheet manually and in parallel.
Computers are used to build the digital maps. When compared to other digitizing methods, it is not only faster but also more accurate. The spatial accuracy level that a human hand can resolve is around 40 DPI (dots per inch) in the best situation, and will be lower if the operator becomes weary or bored after working on it for a long time.
There are numerous advantages to manual digitization.
- Low initial investment, for example, digitizing tables is inexpensive;
- flexibility and adaptation to various data kinds and sources; and
- It’s a skill that’s simple to teach and master in a short length of time.
B. Heads-up Digitizing
A map or image is scanned into a computer using this method. The digitizer then uses digitizing software to trace the points, lines, and polygons.
Because the user’s emphasis is up on the screen rather than down on a digitizing tablet, this type of digitizing is called “heads-up” digitization.
By tracing one line at a time under the instruction of the operator, the interactive tracing method automates the individual line tracing procedure. In terms of digitizing accuracy and speed, this is a major improvement over manual heads-up digitizing, especially when fully automatic raster to vector conversion is not possible, as in the case of low image quality and complicated layers.
The flexibility of tracing lines selectively and enhanced operator control are the key benefits of adopting interactive tracing.
1. Low labor costs;
2. Excellent data quality;
3. Digitizing equipment that are very dependable and often provide more precision than the data warrants; and
4. The ability to easily register and update existing data.
C. Automatic Raster to Vector Conversion
Automatic digitizing, also known as automated raster to vector conversion, uses image processing and pattern recognition algorithms to automatically trace lines from a scanned raster image.
The goal of the automated raster to vector conversion procedure is to enable the computer handle the actual line tracing and eliminate the time-consuming manual tracing that a human operator must accomplish. It has been a key research priority for the past two decades due to the relevance of automating the raster to vector conversion process and the difficulties involved.
there are fundamental restrictions Scanners have a number of other practical constraints.
- Most companies or organizations cannot afford their own scanning device and must therefore submit their maps to a commercial firm for scanning; hard copy maps are frequently unable to be transported to a location where a scanning device is available;
- Hard copy data may not be in a scannable format, for example, maps that are of poor quality or in poor condition;
- There may be too few geographic features on a single map to make scanning viable and cost-justifiable;
- On busy maps, a scanner may be impossible to discern the characteristics to be captured from the surrounding graphic information, such as dense contours with labels; with raster scanning, it is difficult to properly read unique labels (text) for a geographic feature.
- scanning is much more expensive than manual digitizing, considering all the cost/performance issues
D. Interactive Tracing Method
The interactive tracing method is a more advanced version of the Heads-up digitizing technology. It performs admirably in terms of accuracy and quickness.