Tel: +233244686784 /+233208254022
Hanger 2 Kotoka International Aiport -Accra

P.O. Box 5484, Accra-North

Contour Digitizing



An interactive general purpose semi-automated digitizing program developed by IGG for all types of paper maps. Information is digitized from spatially incorrect maps and morphed to move the digitized locations to their correct latitude & longitude plus UTM locations.

Main Digitizing Program

The image above shows the MapDIG contour digitizing capability. There are 4 windows in the image. The upper left windows is the zoom window that gives the operator a zoomed-into view of the area of the map he is working on. The lower left window shows the entire map being worked on with a rectangle superimposed on it showing the location of the map on display in the center window. The center window is the window the operator performs the digitized in. The digitized contours are painted out in a contrasting colour(blue). theĀ  right window contains the controls the operator uses to perform the digitizing with.

Digitizing Controls


The operator uses these controls to initiate contour digitizing. The controls allow the operator to specify the contour value associated with the contour line. The arrowhead buttons are used to tell the program the direction the auto line following algorithm should use to digitize a contour line. Contour lines segments and spots values may be digitized with there controls.

Reference Line

The contour digitizing capability in MapDIG has a feature called a reference line that makes the contour digitizing operation faster and more economical to perform. The reference line feature allows the operator to digitize a sequence of contour lines with minimal operator intervention.


The editing capabilities in the MapDIG contour digitizing program allow the operator to remove or modify single points. a group of digitized points. single contour line segments or a group of contour lines.

Automatic line following




Rotation, Scaling & Translation



The accuracy achieved by digitizing contours from maps scans largely depends on two different things:

The scanning density of the map images.
The type of distortion that exist in the map scans.

The scanning pixel density of image is measured in Dots Per Inch or DPI. Accurate digitizing can be done from maps scanned at a density of 150 DPI or higher. The scanner used should have an accurate feed mechanism. The rollers should feed the map through at a constant rate. The scanner should generate pixels that are spatially equidistant in both the X and Y direction.


Two types of maps may be digitized, colour and monochrome contours maps. monochrome maps needs only be scanned in 1 bit per pixel black and white. For best results with colour maps they should be scanned in 24bit red green and blue colour. IGG will analyse the contours in the scan and reduce the scan to 16 colours while concentrating on retaining the contour information in a single colour. MapDIG performs its fastest and more accurate auto line following if the contours that drawn on the map have a unique colour. monochrome contour maos with underlying topography and other line work tend to be less accurate because of the possibility of artifacts being generated where lines cross.


With colour and monochrome contour maps the auto line following algorithm always generated a point in the middle of the spread of pixel in the contour line regardless of how many pixels wide of thick the line is. The error is always within +/- 1 pixel or +/-1/150th of an inch of the center of the contour line.


Coordinates from distortion free maps are trans formed into geographic and cartographic coordinates using rotation scaling and translation. Linear and non-linear distortions in contour map scans are corrected through using IGG’s proprietary method of triangle morphing. Triangulation density used vanes from map to map depending on the severity of distortion.




  • Accurate and Fast and Economical contour digitizing.


  • Map distortions corrected through triangle morphing.


  • Suitable for any kind of contour map that can be scanned.


  • Contours digitized from a suite of maps may be merged.


  • Output: ArcView shp files, digitized points with geographic references, data grids, contour plots at different scales combined with other data, Flight line or ground survey paths may be threaded to extract line data.