Recently, I have partially re-implemented
the Urban Growth Model (UGM) that was developed by Clarke, Hoppen and Gaydos
using Netlogo. The study area is the City of Santa Fe in New Mexico, USA.
Here is a picture showing the simulation
results after 10 periods:
A video recording a simulation process of
the model can be found here:
The code and data could be found here:
<https://github.com/YangZhouCSS/Urban_Growth_Model>
The image below shows the road types and landuse types in the area studied.
The image below shows the road types and landuse types in the area studied.
In this post, I will briefly talk about how
I re-implemented the UGM using Netlogo. The purpose of this model and this post
is to assist people who are interested in urban growth and urbanization as well
as those interested in learning Netlogo.
The urban growth dynamic implemented in the
Urban Growth Model (UGM) contains four types of growth, namely:
(i) Spontaneous Growth - defines the
occurrence of random urbanization of land.
(ii) New Spreading Centers - determines
whether any of the new, spontaneously urbanized cells will become new urban
spreading centers.
(iii) Edge Growth - defines the part of the
growth that stems from existing spreading centers.
(iv) Road-Influenced Growth - agents take a
road trip along a transportation infrastructure and look for suitable space for
urbanization.
Note: Self Modification is not included in
this model.
More information regarding the growth
process can be found on the project website:
The original paper of the theory of the UGM:
The codes to implement the four types of growth
are relatively easy. I would like to talk about the codes that solve the
following problems:
1.
How to load GIS data (usually a
map) into Netlogo?
The GIS extension of Netlogo allows users
to load .asc data into Netlogo. A map can be converted into .asc files in ArcGIS
using the tool called “Raster to ASCII”. This process will convert a map into a
grid file which contains the size and location information of the whole grid as
well as information of each cell.
Here is an example about how to import .asc
file into Netlogo:
set urban-dataset gis:load-dataset "data/urban_santafe.asc"
Here I created a global variable called urban-dataset
and load the data file into the global variable using “gis:load-dataset”.
Then I have this line:
gis:set-world-envelope gis:envelope-of urban-dataset
“gis:set-world-envelope gis:envelope-of” is
a shorthand for setting the transformation by mapping the envelope of the
NetLogo world to the given envelope in GIS space, while keeping the scales
along the x and y axis the same.
To copy values from the given raster
dataset to the given patch variable in Netlogo, I use this line:
gis:apply-raster urban-dataset urban
Note that the grid size in Netlogo is exactly
the same as the original data, meaning that they have same numbers of rows and
columns.
2.
How to export the results as .asc
files so that we can edit it in ArcGIS?
The following codes are used to export the
.asc file.
The first few lines with “file-print” are
asking Netlogo to write the beginning of the .asc file. This part should be
identical to the original data, since we did not modify the size of the grid.
The while loop asks patches in row i to
write their urban variable into result.asc file. As i decreases from 393 to 0,
we are going through the rows from the first row on top to the one at the
bottom.
I wish you are enjoying this post!
Reference:
GIS Extension for Netlogo. <http://ccl.northwestern.edu/netlogo/docs/gis.html>
