Spatial diffsion over a hexagonal grid

 This model shows how it is possible with Simile to disaggregate a land area into a grid of hexagons instead of the squares normally used, and display results using a polygon diagram. Hexagons have many advantages, including being better able to model lateral diffusion because all the neighbours of a cell are at the same proximity. This model has an inter-cell flow in one direction only, representing the movement of biomass in a situation where seed dispersal happens only in one direction. The hexagon centre coordinates are generated by a parametric method from the model indices, and an existence condition used to restrict the model to its hexagonal boundaries. The coordinates of the vertices of each hexagon are calculated in a 6-instance submodel by adding a set of offsets to the centre coordinates of each hexagon. This enables the polygon helper to get its display information from the model, although the same data could be stored in a separate file instead.