Version: ðŸš§ 2024-06 ðŸš§

# 4. Weight for Road Network

The present model will introduce how to design a road system, or graph, based on the road GIS data and provide each edge a `weight` representing the destruction level of the road.

## Formulationâ€‹

• Add a `destruction_coeff` variable to the `road` agent. The value of this variable is higher or equal to 1 or lower or equal to 2. At initialization, the value of this variable is randomly defined between 1 and 2.
• In the road network graph, more a road is worn out (`destruction_coeff` high), more a `people` agent takes time to go all over it. Then the value of the arc representing the road in the graph is equal to "length of the road `*` destruction_coeff".
• The color of the road depends on the `destruction_coeff`. If "destruction_coeff = 1", the road is green, if "destruction_coeff = 2", the road is red.

## Model Definitionâ€‹

We add a `destruction_coeff` variable which initial value is randomly defined between 1 and 2 and which have a max of 2. The color of the agent will depend on this variable. In order to simplify the GAML code, we define a new variable `colorValue` that represents the value of red color and that will be defined between 0 and 255.

``species road  {    float destruction_coeff <- rnd(1.0,2.0) max: 2.0;    int colorValue <- int(255*(destruction_coeff - 1)) update: int(255*(destruction_coeff - 1));    rgb color <- rgb(min([255, colorValue]),max ([0, 255 - colorValue]),0)  update: rgb(min([255, colorValue]),max ([0, 255 - colorValue]),0) ;    ...}``

In GAMA, adding a weight for a graph is very simple, we use the `with_weights` operator with the graph for left-operand and a weight map for the right-operand. The weight map contains the weight of each edge: [edge1::weight1, edge2:: weight2,...]. In this model, the weight will be equal to the length of the road (perimeter of the polyline) its destruction coefficient.
``    init {        ...        create road from: shape_file_roads ;        map<road,float> weights_map <- road as_map (each:: (each.destruction_coeff * each.shape.perimeter));        the_graph <- as_edge_graph(road) with_weights weights_map;        ...    }``
``https://github.com/gama-platform/gama.old/blob/GAMA_1.9.2/msi.gama.models/models/Tutorials/Road%20Traffic/models/Model%2004.gaml``