# Geographic Information Systems

Spatial Data Modelling

## Mark Foley

mark.foley@dit.ie

# Modelling spatial data

- Learning Outcomes
- Define spatial data model
- Explain how spatial entities are used to create a data model
- Examine raster and vector formats and how they are stored on a computer
- Describe a spatial data structure
- Explain what topology is and how it is stored on a computer

# Introduction

- GIS Model
- Spatial form
- Structure & distribution of features in geographic space

- Spatial process
- Interaction between the features is considered

- We'll concentrate on form for the moment

# Spatial data models

- Raster
- Tessellation
- Cell is building block for creating images of point, line, area, network and surface entities

- Vector
- 2-dimensional Cartesian (x,y) coordinates
- More complex shapes require more points to represent them
- Too few points: measures of length, perimeter area compromised
- Too many points: duplicate information â€“ costly to store and manage

# Building a model

- Identify spatial features from the real world that are of interest in the context of the application and choose how to represent them in a conceptual model
- Represent the conceptual model by an appropriate spatial data model (raster or vector)
- Select the appropriate data structure to store the model within the computer