Computer Security - Data quality GIS is a garbage magnifier...

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Data qualityGIS is a garbage magnifier (Garbage in / garbage out)Most failed GIS projects are due to poor planning and poor data qualityWhenever you work with spatial data (or any data for that matter) you willdeal with some sort of error due to the many steps involved in creatingspatial data.Spatial data is just an abstraction of what is really there.Because of thisabstraction, we can expect error due to:i.How we conceptualize the data in the first placeii.How we collect the dataiii.How we present the data
Data qualityThe following criteria are used when analyzing the internal data quality:1.Accuracy:is the degree to which information on a map or in a digital databasematches actual/ true values.The discrepancy between the encoded and the actual value of a particularattribute for a given entity is defined as an “error”.Types of accuracyi.Positional accuracy-a term used for the degree by which positions on amap or in a GIS database are recorded correctly with respect to theirtrue location on the earth’s surface.For example, accurately measured GPS coordinates will fall into the wrongadministrative boundaries due to wrong positions of the boundaries inthe base map.
Data qualityi.Positional accuracy-It is divided into two different categories:Absolute accuracy:refers to the actual X,Y coordinates of a geographic object.If one knowsthe correct position of the geographic object, they can compare the differences with theposition represented in the geographic database.Relative accuracy:refers to the displacement of two or more points on a map (in both thedistance and angle), compared to the displacement of those same points in the real world.The figures on the below show two different maps of the Cornell campus and the City of Ithaca.The leftmap, a USGS quadrangle, has an absolute accuracy of around 40 feet.That is, the coordinates for abuilding on the quadsheet are probably within 40 feet of their real world coordinates.The right map, aphotogrammetrically derived map of the same area has an absolute accuracy of about 2.5 feet.
Data qualityii.Temporal accuracy- refers to the agreement between encoded and‘actual’ temporal co-ordinates of an entity. Temporal coordinates areoften only implicit in geographical data, e.g., a time stamp indicating thatthe entity was valid at a precise time.iii.Thematic accuracy- refers to the correctness of the descriptiveinformation linked to the spatial data (attribute) values encoded in adatabase.iv.Logical accuracyonly pertains to correct representation/ the integrity ofrelationships among geographic features. For instance, a river in one GISdatabase layer must connect to a bridge in another layer. Anotherexample, a river stored in a hydrologic database that defines theboundary between two administrative units should coincide with theunits in a neighboring map.

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Term
Fall
Professor
Mohammad Alizadeh
Tags
Cartography, Geography, spatial data, Geographic information system, Data Quality

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