Rajan, KS 
  
The model also accounts for the initial cost incurred in land conversion from other uses to agricultural lands. The other 
incomes considered are the non-yield-on-farm income and the off-farm income. These factors influence the decision 
making process, in case of fluctuating agricultural revenues from a given unit of the land. 
3.3 Demand for New lands 
The demand for new agricultural lands are calculated based on the demand for the seven major agricultural crops, in 
case of Thailand. Sugarcane and Cassava are used to represent the cash crops, while Paddy, Maize, Sorghum, Soybean 
and Mungbean are considered as the major crops. The demand also considers the reduction in the land supply due to 
changes to other land uses. 
4 URBAN LAND USE/COVER 
A simplified urban land expansion model has been adopted to understand its spread, due to changes in the population — 
natural growth rate of the population, readjustment in the urban population, and the rural-urban migrations that take 
place; and economic levels of these areas. The population figures are obtained from the migration sub-model and the 
changes in population density are used as the main factor in determining the demand for new urban lands. The model 
finds the existing urban areas, ranks them according to their sizes and density of population first; then goes on to 
calculate the expansion needs of each city individually. The model takes into account the locational value — 
neighbourhood and accessibility of the land-unit in assessing the new areas that will be urbanized. The model assumes 
that all the extra land needed for the urban areas in a given year is fulfilled in the next year. This also for some realistic 
calculations on the changes in the areal extent and locating such changes. The model provides information on the urban 
land demand and supply, on a spatial basis. In case of Nan province, in the North of Thailand, between the year 1980 
and 1990 the model simulated a rise of urban grids from one grid to five grids, whereas the existing land use map of 
1990 showed the existence of four grids. 
5 DEMOGRAPHIC CHANGE 
Population changes on an annual basis are tracked, to provide information on the demands they generate in the various 
sectors. The population at any given location can be considered as a sum of its natural growth rate and the migration 
tendencies. We have adopted the following simple population growth model, 
p —p, © (V@\eut - 1) () 
where, LL is the national population growth rate at initial time reference t; and is the exponential decreasing rate of 
national population growth. 
It is assumed that the national population growth rate can be uniformly applied for the entire country in the absence of 
any detailed information at the individual grid levels. The agent decision model calculates the migratory population 
from or to the respective grid cell. 
6 AGENT DECISION MODEL 
The most important part of the entire modelling framework, is this model. There are two major decisions that the agent 
can make — (i) change in the land use; and (ii) changes to population in the grid. It can be described as a rule based 
model that takes into account the results from all the other models and sub-models, compares it with their preceding 
values and/or the expected benefits thereof, along with the local conditions and preferences to analyse the information 
and make a decision on - (i) whether to continue the current land use or undergo a change; or (ii) relocate some of the 
population and drive land use changes in the subsequent time frame. So, this model compares both the spatial 
information and their aggregated values to arrive at a decision. 
The Rural economy usually consists mainly of the agricultural income. But, in addition to it, the farmers and their 
households also undertake various other part-time occupations during the off-season, or are continuously deriving some 
form of an additional income by engaging in other occupations like poultry and dairy farming and so on. To account for 
these additional incomes as a means of cross-subsidizing their main agricultural income, it is essential to include such 
factors in understanding the rural economic structure. A look at the Figure 4., would help the reader better understand 
the income structure of the rural economy. Figure 4(a) refers to the income structure of the grids that are located around 
the Urban area — it is observed that these grids have a substantial part, nearly 50% (in grids growing paddy and maize) 
to 66%(in grids growing maize), of their incomes coming from off-farm sources of income. The only grid that gets 
more than 50% of its income coming from the agricultural revenue is the grid no.4, where the land use is Paddy. This 
  
1216 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.