Digitization Errors In GIS

In GIS data digitization service, digitization is the process of converting geographic data from either hardcopy or scanned copy into vector data. Features from the traced map or image are captured as coordinates in point, line, or polygon format for the digitization process.

Types Of Digitization:

There are various methods of performing data digitization

1. A manual method involves a puck (a type of specialized mouse) which is used to trace geographical features from an external digitizing tablet.

2. Heads up digitization include tracing of geographical features from another data set like a scanned image, aerial image, or satellite image of a map.

3. Automated digitization involves software that generates vectors by recognizing patterns.

Types Of Digitization Errors:

As most of the digitization involves interpretation of geographical data with human hands there are several types of errors that indulge into the vector. The type of error that happens when a feature is not captured properly is called a positional error, whereas attribute error occurs when information about any of the features is inaccurate.

Here is a list of the major positional errors while digitization:

Dangling Nodes:

Dangling nodes are the lines that haven’t been met, or there is a gap between the nodes. Dangling nodes can also occur when a digitized polygon doesn’t connect back to it.

Switchbacks, knots, and loops:

These errors are introduced with an unsteady hand. With the wrong movement of the cursor/ puck, the line being digitized ends up with extra vertices/nodes. In the case of switchbacks, extra vertices result in a line with a bend. With knots and loops, the line folds onto itself forming a polygon, also known as a weird polygon.

Overshoots and Undershoots:

When a line doesn’t connect properly where it is meant to connect it results in an error like overshoots or undershoots. During digitization, a snap tolerance is set by any digitizer. The snap tolerance or the snap distance is the measurement of the diameter from the point of the cursor.

Any nodes near the line that is inside the circle formed within the snap tolerance are automatically connected to the node this result in overshoots and undershoots. The main reason for undershoots and overshoots could be either that the snap tolerance is not set by the digitizer or the snap distance is set too low.

Silvers:

Silvers are the gaps formed between two adjoining polygons. Setting the snap tolerance properly is crucial in avoiding a silver error.

Conclusion:

Errors while digitization is common and scales from small error to bigger. Most of the errors like silver, dangling nodes can be easily get ridden off with small precautions.

Polosoft Technology provides GIS data digitization services  trusted by many industries, the services mainly include:

• 2D and 3D Digitization
• Paper to CAD Conversion
• Raster to Vector Conversion

There are also other services like:

GIS Mapping

GIS Data Conversion

Digital Photogrammetry