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Areas
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Most of what a schematic is all about is in the list of areas it defines. An area is a location on the diagram where accident graphics may be placed. After its physical location, the most important attribute of an area is the 'condition'. The condition is a filter expression that determines which accidents will be grouped here. A simple condition for an area located in the southbound lanes approaching the diagram from the north might be ( dir_travel = south ) & ( dir_from_int = north). This simplistic example needs some enhancement to be used, but what it says is "this area will hold all accidents whose direction of travel is south, and whose direction from the intersection is north". More on conditions later.
All of the remaining attributes relate to the location of the area. An area's location is defined by a point where the first accident is placed when it fits the condition. The next accident is placed a specified distance from the first accident. The area may define an angle at which to offset each accident; a width at which to 'wrap' accident to a new row; a rotation angle for accidents within the area; a scale. The area also defines the placement of accident labels relative to the accident graphics.
As each accident is added to a diagram schematic, it is checked against the conditions of all the areas in that schematic. When an accident fits the condition of an area, it is added to that area. The exact position is then determined by using the location attributes of that area. An accident will be placed in the first area which it fits, and can not be placed in more than one area.
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