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Spatial Data Entry via Digitizing

Spatial Data Entry via Digitizing. Digitizing. Process of collecting digital coordinates Common data entry method Process by which coordinates from a map, image, or other sources are converted into a digital format in GIS. Digital spatial data. Data in computer compatible format Text files

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Spatial Data Entry via Digitizing

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  1. Spatial Data Entry via Digitizing

  2. Digitizing • Process of collecting digital coordinates • Common data entry method Process by which coordinates from a map, image, or other sources are converted into a digital format in GIS

  3. Digital spatial data • Data in computer compatible format • Text files • List of coordinates • Digital images • Coordinate and attribute data in electronic file format • Common source of digital information

  4. Digitizing Methods • Manual digitization Human guided coordinate capture from a map or image source • On-screen digitizing (heads-up digitizing) • Hard map digitizing

  5. Characteristics of Manual Digitizing • Data accuracy may be affected due to • Equipment characteristics • Abilities and attitude of person digitizing • Map scale • may negatively affect the positional quality of spatial data • Greater for smaller scale maps • Effect of 1 mm on different scales • Table 4-1

  6. Digitizing Process • Display image on screen • Trace locations of feature • Point • Features that are viewed as points • Line • linear features • Starting point is called ‘starting node’ • vertices: intermediate nodes • Ending node • Polygon

  7. Digitizing Errors Positional errors are inevitable in manual digitization • Undershoots and overshoots • Common error of digitization • Undershoots: nodes that do not quite reach the line or another node • Cause unconnected networks and unclosed polygons • Overshoots: lines that cross over existing nodes or lines • May cause difficulties in network analyses

  8. Node and Line Snapping • To reduce undershoots and overshoots while digitizing • Snapping: process of automatically setting nearby points to have the same coordinates. • Relies on a snap tolerance or snap distance • Prevent a new node from being placed within the snap distance of an already existing node – new node is joined or snapped to the existing node ensuring connection between digitized lines

  9. Reshape: Line Smoothing and Thinning • Software may provide tools to • Smooth • Densify • Thin • Spline Function • To smoothly interpolate curves between digitized points

  10. Scan Digitizing

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