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Acquiring GIS Data: Utah |
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Introduction: GIS data come in a variety of forms i.e. raster, vector, TIN and analog. Raster data are images, grids, or other continuous surface data which are pixel based. Vector data are comprised of points, lines or polygons; points being the foundation of all vector datasets. A line contains a beginning and ending point and enough intermittent points (vertices) that help define the shape of the given line. Polygons are made from a line or a grouping of lines that begin and end in the same location. TIN data are Triangulated Irregular Networks that form surfaces, which are made up of nodes and edges which form miniature triangular surfaces. In this exercise we will not be working with TIN data. Analog data are information contained in various non-spatial forms. For example, an address is just information; but in GIS, that information can be redistributed through a process called geo-coding or geo-referencing, where each address is represented by a point. Additional analog data come in the form of latitude and longitude or northing and easting. Through a process known as an XY event or event theme, these analog data can be recreated as spatial representations (usually points). Major components of GIS are digital data and their associated attributes and/or values. These components are scaled representations of spatial phenomena, which exist in space and time. Data space is represented by an x, y and z location, and occasionally, there can be a temporal (t) value representing some value of time. We will not be discussing temporal relational databases in this exercise. Any spatial object can be represented digitally at variety of scales. For example at a large scale a house might be represented as a polygon, yet at a smaller scale that same house will more than likely be represented by a point. It is up to the person collecting the data to understand their project needs in order to acquire the correct data format at the appropriate scale. By knowing the scale of the data and the amount of ground your project will cover you can get an idea of the amount of data storage that will be required. This will be covered in more detail later. Moving GIS data, and GIS data file storage are accomplished in many ways. The most common method of storage is to use some form of file compression, usually with a zip or tar format, integrated with an import and/or export interchange file option. File compression helps to ease the transfer process by decreasing the size of the file as well as grouping file structures that must be moved as a set. |
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