1 / 9

Introduction

Introduction. GIS is often used to model processes. Two main objectives: To understand how the processes operate; To predict the likely outcomes given particular conditions. Today we will do two things: Look at process models in general Discuss cartographic models. Process Models.

emele
Télécharger la présentation

Introduction

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Introduction • GIS is often used to model processes. Two main objectives: • To understand how the processes operate; • To predict the likely outcomes given particular conditions. • Today we will do two things: • Look at process models in general • Discuss cartographic models

  2. Process Models • Process models attempt to model dynamic processes. May be: • A priori – driven by data rather than theory. Approach is basically inductive. • A posteriori – based on established theory. Approach is more deductive. • Objectives: • Systems analysis • Decision support

  3. Process Models(2) • Process models can be either: • Descriptive / predictive • Prescriptive • Can be thought of as forming a continuum: • Description -> Prediction -> Prescription

  4. Gravity Models • Gravity models provide a good example of a process model. • Basic form: • The model may be fitted to determine the r and k parameters (calibration). • May need to distinguish between source and destination using exponents. • Many uses: e.g. migration, shopping trips, etc.

  5. Cartographic Models • A cartographic model is basically a flow diagram identifying the various coverages required for a particular end result. • For example, suppose we wished to identify suitable sites for a mountain cabin (DeMers). • There are several steps: • Identify our criteria. • Identify the data required. • Identify the types of GIS operation required.

  6. Weighting And Automation • In this example we use simple Boolean overlays – i.e. each criterion exercises a ‘power of veto’. • May be preferable to use fuzzy membership functions and/or weight the various criteria - i.e. weighted linear combination (WLC). • Can produce fewer or more suitable sites by adjusting the weightings. • May be useful to automate the model to allow it test ‘what if’ scenarios more readily. Could write a script or use a tool such as ESRI’s Model Builder.

  7. Pilot Study • In a big study it may be useful to do a pilot study using a sample area: • Can be done rapidly and cheaply; • Results can be ground truthed; • Can identify data that may be discarded if space an issue. • Verification entails checks of: • Accuracy • Usefulness

More Related