Incorporating Cost-Distance Raster

[KBogue13]

I have calculated a cost-distance raster to model land use change. In this scenario, my equation is ln((Euclidian Distance from Growth Center * Elevation) / Population Density) which is meant to model the suspected growth path through a particularly county. I am wondering how to incorporate my cost-distance raster into my STSM and/or how to structure my data in a way that makes this possible.

Thank you in advance for any help.

[leonardo-frid]

Hi Kevin,

If your cost/distance raster is static or defined temporally but independent from the model, you could use it to generate Transition Spatial Multipliers (http://docs.stsim.net/reference/prop_transition_spatial_mults.html) to set the probability of transitions for each cell.

If you would like to build in some feedback between modeled landscape dynamics and your cost/distance raster, you may be able to use the Transition Adjacency Multipliers feature found in ST-Sim (http://docs.stsim.net/reference/prop_transition_adjacency_mults.html). This is an advanced feature that allows you to change transition probabilities as a function of the state of cells within a neighborhood. So for example you could set the probability of an urban growth transition to be 0 when it has no urban neighbors within a 500m radius and increase this probability as a function of the number of urban neighbors within that radius.

[KBogue13]

Thank you so much for your reply, Leonardo.

Funnily enough I actually just finished trying the ‘Transition Spatial Multiplier’ approach you mention above and the preliminary results are encouraging. However, I am extremely interested in building in some feedback and will try the ‘Transition Adjacency Multiplier’ approach in the coming days.

Thanks to you and Colin for the product you’ve put out and the support you offer. Both are very much appreciated.

[colin-daniel]

The other option for introducing a dynamic link between a cost/distance function of yours and the transition probabilities in ST-Sim is to use the Spatial Transition Multipliers in conjunction with the External Program feature. This would allow you to pause the ST-Sim simulation throughout the simulation and turn control over to a script of your choice (e.g. in R or Python). Your script could then read in the current ST-Sim raster projections for the state of your landscape at the time of the pause, calculate a new Spatial Transition Multiplier raster for the next timestep however you like, and then pass the new Spatial Transition Multiplier raster back to ST-Sim. In this way you are dynamically modifying the transition probabilities across every cell, timestep and Monte Carlo realization as the simulation progresses. The rsyncrosim R package can help you move data back and forth between SyncroSim and an R script. In Python you can make calls to the SyncroSim command line API to do the same. Note that your simulations will take a performance hit for using this feature, as data is passed back and forth between SyncroSim and script by disk.

Below is an example of how you might set this up using the SyncroSim Windows UI for a call to an R script every 5 years in the simulation. Full online documentation for this new feature is coming soon.

[KBogue13]

Thanks so much, Colin.

I am currently working on incorporating the adjacency multipliers but will look into the ‘External Program’ option next.

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