Modeling population growth and the
implications of urban expansion in

INTRODUCTION

Figure 1: Extent of forest cover in

The government of

Figure 2: The
Protected Areas of Belize,

The wide variety of environments
represented in these protected areas hope to maintain the integrity of
biodiversity and rare species within the country. Conserving the natural
environment in

Although the government of

OBJECTIVE

My intent for this term project was to
use ArcGIS (version 9) to address development in

1. Predict the increase of

2. Show the distribution of an estimated population increase for each district.

3. Demonstrate how predicted population
growth would compromise designated
Protected Areas.

DATA FOR

Finding
geographical datasets for international countries can be more challenging than
using regional data sources such as USGS. Information is not always up to date
and it can be saved in files that are not compatible with ArcGIS.
The best source for my basemap data was downloaded
from the Digital Chart of the World website in the form of a zip file that
contained relevant features saved in interchange format (extension .e00). I
created a new geodatabase in Arc Catalogue called
‘Belize’ and using the ArcToolbox function *Import features from Interchange file*, I
added each feature class to a feature dataset ‘BelizeUTM’
so that each layer would have the same UTM projection (Figure 3).

Figure
3: Using the *Import to Interchange File*
tool in ArcToolbox.

I originally had a lot of difficulties
opening this data as the import function kept rejecting my output files. This
was reportedly caused by operating ArcGIS on a vast
network and I was able to successfully import the data by saving the converted
files in a temporary folder on the local hard drive. I also obtained a polygon
feature class from Jan Meerman (Biological Diversity
in

I
hoped to find Digital Elevation Model and satellite imagery land use datasets,
however the region I focused on was extensive (22 ,966 km^{2}), making DEMs
from sources such as SRTM too large and there was no adequate land-use data
available.

Population data and current growth rate
was acquired from the Government of Belize. I used 2000 and 2004 census data
(Central Statistical Office) as archive and current populations, respectively.
The population in each of the six districts of

Figure
4: Attribute tables for TotalPopulation and DistrictPopulation feature classes.

DATA ANALYSIS

*Population
Growth*

Population growth can be estimated using
exponential or logistical equations. These formulas take the initial population
*N _{0} *and calculate increases
or decreases over

N_{t} = N_{0}*e^{rt}

or put more simply

Population at time *t*
= Initial population * e^{(}^{growth rate r * time t)}

NOTE:
The exponential growth equation does not take into account immigration,
emigration, or limits to resources and space.

In order to examine population growth in *Editor* toolbar. I estimated the
population of

Figure
5: TotalPopulation model in ArcToolbox
used to calculate the estimated population of

Each step of the model calculates the
predicted population of a year based upon the preceding year’s estimate. This
way I could use the same GrowthRate figure as *t* remained constant. After running the
model, I displayed the population estimates using *Chart - Bar Graph* under Symbology (Figure
6).

Figure
6: Estimated population growth of

*Population
Distribution*

The
six districts of

Figure 7:
Population within each district of Belize for the year 2004.

Figure
8: Population within each district of Belize for the years 2000 and 2004
projected on an ArcMap. The Excel chart indicates the
district proportion of the total population does not change.

I estimated district population growth by
building another model in my

Figure
9: DistrictPopulation model in ArcToolbox
used to calculate the proportion of the population in each district between 2005-2035 in 5 year intervals. (NOTE: The model is
longer than displayed).

I entered the population estimate for
each year because Model Builder could not join these numbers from one feature
class to the other. I could have created redundant fields in the District attribute
table of total population, however entering a single
number into the model saved me time as this dataset was relatively small. If I
was to apply this model to a larger group of districts, I would use redundant
fields to remodel population estimates and calculate district proportion from
the single table. I felt comfortable operating under the assumption that growth
would occur at a constant proportion because this model did not generate any
new data, but merely showed the possible distribution of total population
estimates within the country.

Figure
10: Estimated population growth of each district of Belize for the next 30
years.

*Population
Expansion*

To
determine the effect that population growth would have on sensitive ecosystems,
I looked at how the expansion of city limits would encroach upon neighboring
Protected Areas. The feature class ‘Towns’(from the
Digital Chart of the World dataset) represent single points of populated areas
in

Figure
11: Towns feature class projected on an ArcMap. The
Excel chart indicates the distribution between rural and urban populations for
the years 2000 and 2004.

I
measured population expansion using the *Euclidean
Distance* function in ArcToolbox. By calculating
the distance from each Town to another, I projected growth of these populated
areas in increments of kilometers (Figure 12).

Figure
12: Euclidean Distance function measuring the distance (in meters) between
Towns.

I set the increments to 1000 meters in Symbology and designated radial increases of less than 5 km
as red, orange and yellow (moving away from Town centers).These regions pose
the most immediate threat to endangered ecosystems, as even small settlements
can easily reach diameters of 10 km. Values represented in green are still in
danger of encroaching upon Protected Areas, however, this growth depends
entirely upon the magnitude and direction of urban sprawl. Due to the large
percentage of land designated as parks or reserves, more than half of the Towns
currently lie within 5 km of a Protected Area and all Towns lie within 20 km
(Figure 13). Therefore, if each Town feature expanded up to 20 km, the
surrounding ecosystems would be drastically reduced.

Figure
13: The vicinity of Protected Areas to populated areas in

I
also used the *Euclidean Distance*
function to project the expansion of roads. These thoroughfares connect
populated areas and are associated with construction, pollution, and often
become the first areas to be developed. Population growth would increase the
demand for wider existing roads and the formation of new ones (Figure 14).

Figure
14: The expansion of existing roads and the Protected Areas that they
intersect.

DISCUSSION

I
was able to determine population growth in *Tracking Analyst*.

The
capabilities of ArcGIS are adept at analyzing a
multitude of information, however there are some limitations. To perform any
kind of ecological modeling, users must be able to calculate a variety of
functions. Unfortunately, in the *Calculate
Field* tool complex functions such as exponents and logs are not
possible. A looping function in Model
Builder would also improve efficiency so that data does not have to be entered
repeatedly.

CONCLUSION

This
exercise in ArcGIS gave me the opportunity to
approach estimating the population growth in

DATA SOURCES

This project was completed with helpful
advice from correspondence with Jan Meerman
(Biological Diversity in

ArcGIS version 9x. ESRI 2003.

Central
Statistical Office (Ministry of Finance)

Digital
Chart of the World

http://www.maproom.psu.edu/dcw/

Government
of

Jan Meerman (Biological Diversity in

http://biological-diversity.info/

Joshi,
K.N. and Suthar, C.R. 2002. Changing urban land use
and its impact on the environment (a case study of Jaipur
city).

Protected
Area Conservation Trust

http://www.pactbelize.org/index.php

APPENDIX I: Population Doubling Time

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/P/Populations.html

In
order to estimate the amount of time it will take for a population to double, a
simple calculation can be used.

Growth
Rate of

When a population doubles, N =**
**2N_{0}

Using the exponential growth equation, N_{0}*e^{rt} = 2 N_{0}

Canceling the N_{0} on each side leaves e^{rt}
= 2

Growth rate *r *is known,
therefore solving for *t * rt
= ln 2

Results in 0.69/r

Therefore, doubling time is 0.69/0.0239
= **28.9 years**