Digitizing the Network

After developing the TAZ and NETWORK tables, the next step is for the user to develop the actual model network. To assist in this step, a MapBasic program was written that walks the user through the appropriate steps and automatically enters data for some of the important fields (note that any values entered can be manually changed by the user).

Before running the program, it is important to copy the program into the directory where the new model is going to be developed. It is also important that this directory not have any files named LINKS or NODES because these filenames will be created by the program (overwritten if they already exist). To run the program, open MapInfo and a map showing the background tables that will be used to assist in the model development, for example, the TAZ map, the network map, the Coordinated Management System Database cartography. After running the program, there will be a new menu, MODEL_DEVELOPMENT, on the menu bar and the map window will indicate the inclusion of two new tables, NODES and LINKS.

To begin the program, the user needs to select the first menu option, LOCATE CENTROIDS. This option will provide the user some additional instruction on the placement of the centroids. They information is:



and



At this point the user needs to place points for all the centroids. This is done by using the point tool and clicking the mouse button where ever a new centroid is to be located. Note that it is also important to locate the external stations at this point. The following figure shows the centroid placement.



After locating all the centroids, the user needs to select the next menu item, LOCATE NODES. Selecting this menu option will provide the user another message to instruct them.



At this point the user need to place nodes at the appropriate locations. This is done by using the point tool and clicking the mouse button where ever a node is to be located. Note that it is importation to include all the nodes in the network at this step. Therefore, it might be beneficial to sketch out the network before hand to ensure that no nodes are missed. Another suggestion that will assist the development is to change the symbol style for the nodes to help ensure correct placement. The following figure shows the nodes.



After placing the nodes, the user needs to select the LOCATION LINKS option from the menu. This will display a message to assist the user.



The user then needs to use the line tool and draw the links for the network. Note that it is important to snap the links to the node. This is important because the nodes and links are joined by coordinate values and if they are not snapped, the coordinate will be different and the links will not be numbered correctly. After drawing in the links, the network information will be completed.



At this point, the user needs to select the final menu option, FINISH MODEL DEVELOPMENT. This will update the attribute information for the nodes and links and enter the default values. It is important to remember that the user can change any of the entered default values, such as speed and capacity. Finally, after running the program, the menu will be removed and the program will display the final message,



informing the user that this is the appropriate time to enter the socio-economic data to perform a model run.

The user should either go back to the main bypass page or to the Site Map to continue.