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3.0 Development of Data Base
The data required for the study include zonal details of study area, road network details of study area and traffic volumes on selected links. These data can be classified as graphic and non-graphic data.

3.1 Graphic Data
Presently the graphic data of traffic zones and road network are available in paper form. These paper drawings have been converted into digital maps adopting the following procedure.

The paper maps, which are large in size, were scanned using the setup available in the laboratory. The setup consisted of video camera interface with a computer through a frame grabber card. The map was kept in front of the video camera such that it is perpendicular to the axis of the camera. Using the software for operating the frame grabber card, the image of the map was captured and stored in jpeg format. To have good clarity of captured images, the paper drawings were first traced with thick and dark ink pen. The zonal map and road network map were captured separately.

These captured images were imported into the GIS software MAP, a product of AutoDesk in raster form and were then converted into digital form. For converting raster drawings into digital form the tools or utilities available in MAP were used. Using these utilities three types of objects, nodes, lines and polygons, can be digitized. The raster drawing was kept in one layer and the objects were traced into another layer. After the objects were traced from raster image, the layer consisting of raster image was put off and the file was saved as GIS file. The zonal map and road network were traced into separate layers. The maps of the traffic zones and road network are shown in Fig. 1 & 2 respectively.

Fig. 1 Zonal Map of Calicut City


Fig 2 Road Network Map of Calicut City
During the process of digitization many types of errors crept in. These errors were corrected using the clean up tools available in MAP, such as duplicate objects, erase short objects, break crossing objects, extend undershoots, erase dangling objects, simplify linear objects, snap cluster nodes, dissolve pseudo nodes and edge matching. Thus the graphic data consisting of two layers, one representing zones and the other road network, was developed. In the zonal map each zone was represented as polygon and the road links in road network were represented as linear objects.