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Regional demand
Regional demand, also called a claim, says how much land a land use type needs in a region. It is one of the two inputs of an allocation: suitability says where a type would like to be, and regional demand says how much of it has to end up in each region.
A land use model usually does not derive its own demand. Claims come from sector models and projections outside the model, such as housing and employment models, and they differ per scenario. The land use model then brings the claims of different sectors together and tests whether they fit on the available land.
A claim can also follow from a simple rule. 2UP derives the urban claim of a country from its projected population and population density.
Not every type needs a claim of its own. A common choice is to let agriculture take the land that the other types leave, on the assumption that it has the least spending power in the competition for space.
- An amount, usually in hectares. A claim can give the total area of a type or the area to be added to the current area. Models that allocate objects can also state claims in dwellings or jobs, as RSLight2021 does.
- A region. Each type can have its own regional division. Regions of different types may overlap, but within one type a land unit belongs to one region only. A coarse division leaves the model more freedom to choose locations, and a fine division keeps the result closer to the regional projection.
- A lower and an upper bound. With separate bounds, a claim is a range. When they are equal, the claim is one exact amount.
- A year. Projections are usually given for a few years, and a model can interpolate between them.
All land of a land unit has to be allocated, so the claims can only be met exactly if they add up to the land that is free in a region. If they add up to more or less, not all of them can hold. There are two common ways to deal with this:
- Give claims a lower and an upper bound, so that the model has room to find a solution.
- Let one land use type take the rest, so that the claims of a region add up to the free land before the allocation starts.
A claim that limits the allocation has a shadow price: the tax or subsidy that is needed to keep the type within its claim. In a continuous allocation this is the balancing factor; in a discrete allocation each claim has a comparable shadow price.
The Land Use Scanner demo has claims per province, as hectares added since 2022, for 2030, 2040 and 2050. Agriculture takes the rest in each province. The model interpolates to the year it simulates and adds up the provinces when it allocates per part of the country.
