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Unformatted text preview: ESPM 72 Introduction to Geographical Information Systems Lab: 2-5pm 124 Mulford Thursday February 28 LAB 3 Due: March 13 (at the beginning of the lab period). Lab Objective To gain a clear understanding of what a data model is, and why data models are important. To learn the data models ESRI supports in ArcGIS, and the similarities and differences between them. To learn how to search online data and assemble data from different coordinate systems. To reinforce basic ArcGIS skills. Software Needed ArcGIS, Internet Explorer Description Basic Concepts There are three basic spatial data types used with GIS (points, lines, and areas): * Points represent anything that can be described as a discrete x, y location * Lines represent anything having a length * Areas , or polygons, describe anything having boundaries These data types comprise the vector model, which is the model you will deal with most often in GIS. Vector data model: Discrete features, such as customer locations, are usually represented using the vector model. Features can be discrete locations or events, lines, or areas. Lines, such as streams or roads, are represented as a series of coordinate pairs. Areas are defined by borders, and are represented by closed polygons. When you analyze vector data, much of your analysis involves working with (summarizing) the attributes in the layer's data table. Raster data model: Continuous numeric values, such as elevation, and continuous categories, such as vegetation types, are represented using the raster model. The raster data model represents features as a matrix/lattice of cells in continuous space. A point is one cell, a line is a continuous row of cells, and an area is represented as continuous touching cells. Tabular data: Contain information describing a map feature in the form of a table or spreadsheet. For example, a GIS database of customer locations may be linked to address and personnel information. GIS links this tabular data to associated spatial data. Question 1: Give an example of how a continuous phenomenon can be represented using the vector data model. Geographic Data Modeling: An Introduction Data Model - An abstraction of the real world which incorporates only those properties thought to be relevant to the application at hand, define specific groups of entities, and their attributes and the relationships between these entities. A data model is independent of a computer system. Data models are a crucial concept for GIS users to understand. Data models describe how geographic data will be represented in the GIS. Any time you wish to deal with geographic data in a computing environment, you must choose a geographic data model by which to do it. The choice of data model will yield benefits in terms of simplifying real-world features enough to deal with them easily, but will also incur costs in terms of oversimplifying or misrepresenting different aspects of them in the process. A paper map is an example of an analog data model -- it is a formalized framework that cartographers use to capture...
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