Spatial Data Models 5/7/2018 What are Spatial Data? Spatial analysis vs. geographical information analysis Spatial Data Representations Attribute Data Measurement Scales Environmental modelling is a powerful tool for the management of natural resources. Hydrological modelling is a complex process but it is a major requirement of hydrologists, geomorphologists, engineers, and environmentalists who need to answer rainfall-discharge relationships. © J.M. Piwowar What are Spatial Data? © J.M. Piwowar

Spatial Analysis Spatial data manipulation Spatial data analysis The basic functions of any GIS (e.g. data projection). Spatial data analysis Descriptive and exploratory functions using maps (e.g. overlays). Spatial statistical analysis Uses statistical methods to determine if spatial data are “typical” or “unexpected” relative to a statistical model. Spatial modelling Constructing models to predict spatial outcomes. © J.M. Piwowar What are Spatial Data?

Geographic Information Analysis The study of patterns that arise from processes that may be operating in space. Includes methods and techniques that enable the representation, description, measurement, comparison, and generation of spatial patterns. © J.M. Piwowar What are Spatial Data?

Spatial Data Types What are the 2 fundamental spatial data types? Objects (vector data model) Points, lines, areas Fields (raster data model) Ancient Greek philosophical debate about the nature of reality: Is the world a continuous field of phenomena or an empty container filled with distinct objects? © J.M. Piwowar What are Spatial Data?

Spatial Data Representation Issues Spatial Data Models 5/7/2018 Spatial Data Representation Issues Fields and objects do not adequately represent all types of geographic reality. e.g. networks, image data There is a need to separate the representation of an object from its fundamental spatial characteristics. A line object may be used to mark the edge of an area, but the entity is still an area. Geographic scale is important. Depending on the scale, a railway station may be represented as a point, a set of lines, or an area. Image data An image in a GIS might be a scanned map used as a backdrop Yes, they are coded as rasters, but the attributes (i.e. pixel values) are not important … it is the image as a whole that is useful. © J.M. Piwowar What are Spatial Data? © J.M. Piwowar

Spatial Data Representation Issues The objects to be analyzed are often 2-dimensional, with depth or height as an attribute. Real-world objects exist in 3 spatial dimensions. This view of the world is a static one with no concept of time, except as an attribute. This is fine for some applications, but in may other problems we are interested in investigating how things change over time. Even in this limited world view, the number of geometric and spatial operations is already large. We already have operations involving just points (e.g. distance), just lines (intersections), just areas (containment), or any combination of these. © J.M. Piwowar What are Spatial Data?

Thinking Exercise Examine a topographic map; remember that the map is already a representation of reality. For 10 of the types of entities that are represented on the map, list whether they are best coded as an object or a field. If the entity is to be represented as an object, say whether it is a point, line, or area object. © J.M. Piwowar What are Spatial Data?

Scales for Attribute Description Nominal Categorical; e.g. a satellite image classification Cannot be mathematically manipulated in any meaningful way. Ordinal Ordered data; e.g. a road network Interval Differences between categories are defined using fixed equal units; e.g. temperatures Can be mathematically manipulated. Lack an inherent zero; e.g. does 0°C mean “no temperature”? Ratio Same as Interval, but has an inherent zero; e.g. 0 cm really does mean “no distance”. © J.M. Piwowar What are Spatial Data?

Scales for Attribute Description O’Sullivan and Unwin, 2003. Geographical Information Analysis. Hoboken: Wiley. © J.M. Piwowar What are Spatial Data?