Post on 16-Dec-2015
© J.M. Piwowar 1Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Principles of Spatial Modelling
© J.M. Piwowar 2Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Systems Modelling Approach
The process of breaking down highly complex environments into discrete systems so that it can be more easily studied. Each sub-system will have its own inputs and
outputs and interconnected components. It allows us to focus on that which is of direct
interest; everything else is ignored.
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© J.M. Piwowar 3Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Environmental Systems Environmental systems
exist over a range of scales: microscopic biota through to the Earth’s climate system
At each scale, the individual components have boundaries (e.g. a
leaf’s surface) but are interconnected with other systems at other scales (e.g. sunlight & moisture).
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© J.M. Piwowar 4Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Assumptions
1. It is actually possible to subdivide the real world into discrete, contained, functioning systems.
2. It is possible to determine the various inputs and outputs and interrelationships between system components.
© J.M. Piwowar 5Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Why Model?
A model represents a simplification of reality.The intention is to retain the significant
features and relationships of reality. All models are subjective.
The modeller chooses which real-world elements should be included as well as how they are represented.
Models are used to describe, explore, and analyze how a system works; and to test predictive “what if?” scenarios.
© J.M. Piwowar 6Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Types of GIS Models
There are many different types of model classifications.
Many models can exist in more than one category.
Some models that are separated in one classification may be joined in another classification.
© J.M. Piwowar 7Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Types of GIS Models
Purpose Models Descriptive Models
Describe parts or all of a study area. Passive.
• e.g. a map.
Prescriptive Models Prescribe best solutions. Active.
• e.g. best location analysis
© J.M. Piwowar 8Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Types of GIS Models
Logistic Models Inductive
Builds general models based on individual data. Moves from specific examples to generalized models. Useful if we are unaware of the general conditions or
rules that govern the modelled features. Deductive
Straightforward; easily understood. Logic moves from general to specific. Useful if we already have substantial preliminary
knowledge of what factors are important, how they interact, and which are most important.
© J.M. Piwowar 9Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Types of GIS Models Methodological Models
Deterministic There is only one output for a given input Unique solutions are obtained The simplest type of relationship between 2 variables is linear
• e.g. a = mx + b
Stochastic There are a range of possible outcomes for any one input; there
is no single answer. Reflects randomness, or uncertainty, in the system Uncertainty is incorporated through probability
• e.g. Markov models: the probability of an event occurring is dependent on the event preceding it.
Monte Carlo simulations: take random samples from a stochastic model; the results are independent of previous states of the system
© J.M. Piwowar 10Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Types of GIS Models
Deterministic Inductive Descriptive
© J.M. Piwowar 11Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Types of GIS Models
Stochastic Inductive Prescriptive
Descriptive
© J.M. Piwowar 12Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
Ideal Model Properties Generality RealityPrecision
Only 2 can be adequately represented in any given model.
Analytical or mathematical models focus on generality and precision and predict accurate response within a simplified reality.
Mechanistic or process models are realistic and general and base predictions on functional cause and effect relationships.
Empirical models are precise and realistic and are based on empirical facts.
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© J.M. Piwowar 13Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
The Modelling Process
State ObjectivesThe first step in model
conceptualization is to think about the end results … what do we want the model to produce?Care must be taken to provide an objective
result rather than prescribing the outcome to fit expectations.
© J.M. Piwowar 14Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
The Modelling Process
Define Model ComponentsDivide the problem into elements and
operators.Recognize spatial patterns.Identify the processes that created the
patterns.Look for linkages.
© J.M. Piwowar 15Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
The Modelling Process Find Data
Find data to work with your model; do not make your model work with your data.
Reasons to ignore existing data:They may not have the necessary scale,
accuracy, classification, etc.They may not have the desired spatial
coverage and/or employed appropriate sampling procedures.
They may have too many themes.Data sets can often bias your thinking.Many data sets are incomplete.
© J.M. Piwowar 16Geog 409: Advanced Spatial Analysis & Modelling Principles of Spatial Modelling
The Modelling Process
Recognize Spatial PatternsSometimes determining the underlying
processes that created the patterns; sometimes evaluating the effects of existing patterns on on-going processes.
Go beyond pattern recognition into pattern description.
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