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UNIT 3 – MODULE 3: Raster & Vector SPATIAL DATA MODELS • A spatial data model represents real-world conditions within a GIS by relating geographic features. • There are two primary ways that data is modeled: raster and vector. Credit: BiodiversityGIS * * RASTER • A collection of cells (pixels) that are organized into rows & columns, making up a grid. • Information is contained within each cell: location and value. • Satellite & aerial images are already formatted as a raster (e.g. thematic, surface and basemaps). Credit: CUNY VECTOR • Made up of points, lines and polygons. • This model uses Cartesian coordinates (x,y) to store a spatial entity’s shape. • Points represent the simplest spatial entity, and lines connect points to form polygons • More complex line shapes mean more points are required to represent it. Credit: www.lyzidiamond.com RASTER VS VECTOR Credit: Indiana University * MORE RASTER VS VECTOR Credit: www.landsurveyorsunited.com Credit: City University of New York Credit: Penn State SPATIAL DATA STRUCTURE: RASTER Credit: www.innovativegis.com SPATIAL DATA STRUCTURE: VECTOR Credit: www.innovativegis.com RASTER PROS & CONS • Advantage – Simplicity: data structures are simple, as are implementation of overlays. – Very efficient for image processing. • Disadvantage – Data structures are less compacted. – Topology is difficult to represent. – Feature boundaries & cell boundaries are not merged. VECTOR PROS & CONS • Advantage – Good at representing topology. – Can be adapted easily to scale changes. – Can be used easily with attribute data. • Disadvantage – Data structures are very complex. – More difficult to overlay data. – Difficulties with image processing. – Requires constant updating.