What are Spatial Data Spatial analysis vs geographical

What are Spatial Data? § Spatial analysis vs. geographical information analysis § Spatial Data Representations § Attribute Data Measurement Scales © J. M. Piwowar Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 1

Spatial Analysis § Spatial data manipulation v The basic functions of any GIS (e. g. data projection). § Spatial data analysis v Descriptive and exploratory functions using maps (e. g. overlays). § Spatial statistical analysis v Uses statistical methods to determine if spatial data are “typical” or “unexpected” relative to a statistical model. § Spatial modelling v Constructing models to predict spatial outcomes. © J. M. Piwowar Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 2

Geographic Information Analysis § The study of patterns that arise from processes that may be operating in space. v. Includes methods and techniques that enable the representation, description, measurement, comparison, and generation of spatial patterns. © J. M. Piwowar Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 3

Spatial Data Types § What are the 2 fundamental spatial data types? § Objects (vector data model) v Points, lines, areas § Fields (raster data model) § Ancient Greek philosophical debate about the nature of reality: v Is the world a continuous field of phenomena or an empty container filled with distinct objects? © J. M. Piwowar Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 4

Spatial Data Representation Issues § Fields and objects do not adequately represent all types of geographic reality. Ø e. g. networks, image data § There is a need to separate the representation of an object from its fundamental spatial characteristics. ØA line object may be used to mark the edge of an area, but the entity is still an area. § Geographic scale is important. Ø Depending on the scale, a railway station may be represented as a point, a set of lines, or an area. © J. M. Piwowar Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 5

Spatial Data Representation Issues § The objects to be analyzed are often 2 -dimensional, with depth or height as an attribute. Ø 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. Ø 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. Ø © J. M. Piwowar We already have operations involving just points (e. g. distance), just lines (intersections), just areas (containment), or any combination of these. Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 6

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. v If the entity is to be represented as an object, say whether it is a point, line, or area object. © J. M. Piwowar Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 7

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 • Cannot be mathematically manipulated in any meaningful way. § 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 Geog 409: Advanced Spatial Analysis & Modelling What are Spatial Data? 8