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UNC-Chapel Hill GEOG 070 - LECTURE NOTES

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Mistake in textRepresenting Scale on MapsScaleScale is a ratioGeneral Classification of ScaleScale and Map ProjectionsScale Varies on a MapScaling UpMaps and GIS - Scaling UpSlide 10Slide 11Maps and GIS - Scaling DownSlide 13Intended useExamplesMistake in textMistake in text•Page 55:•Chain coding:•4,3 1•N,2 E,4 S,1 E,1 S,1…2 should be 1.Definition:The scale of a map is ratio between distances on the map and the corresponding distances in the real world.Representing Scale on MapsRepresenting Scale on MapsScaleScale•Scale representation on the map:–Representative fraction (RF): “1:100,000”, “1 to 100,000”, or “1/100,000”–Verbal: 1 inch is equal to 50 miles–Graphic: Scale bar10 milesScale is a ratioScale is a ratio•Scale of a map is a ratio •It is unit-independent•1/1000 > 1\100,000 –(1/100 is greater than 1/100,000)•Thus 1:1000 is a large scale map, showing a smaller region but magnified•1/100,000 is a small scale map, showing a larger region•Remember that the notions of small and large are reversed from our conventional thinking when we talk about scale  large scale refers to looking at a smaller area in detail.•Here are some scale guidelines:–Large scale  1:400 to 1:50,000–Intermediate scale  1:50,000 to 1:250,000–Small scale  1:250,000 and beyondGeneral Classification of ScaleGeneral Classification of Scale•The representative fraction of a map does not tell us the scale everywhere on the map! •Transformations due to projecting maps introduce distortion–RF is only accurate along standard lines or pointsScale and Map ProjectionsScale and Map ProjectionsScale Varies on a MapScale Varies on a Map•Does the same length measured on the map at the Equator and near the pole represent the same distance?• The map scale (RF) is only valid along these standard linesStandard linesScaling UpScaling Up•Data created for local areas can be used for larger (regional or national) areas.Maps and GIS - Scaling UpMaps and GIS - Scaling Up•The river network shown here on a national scale was produced at a much larger scale, and it contains a great deal of detail that cannot be seen here … zooming in …Maps and GIS - Scaling UpMaps and GIS - Scaling UpAll the detail that is encoded in this river network data is really only visible and useful when operating at more local scales.This level of detail is not necessary or useful at the national scale. Vector data such as this river may need to be smoothed for scaling up.WhitepineLodgepolepinericewheatScale Effect on MappingWhitepineLodgepolepinericewheatWhat should we call these cells?Scaling upMaps and GIS - Scaling UpMaps and GIS - Scaling UpRaster data may need to be generalized. An aggregation algorithm must be chosen. (aggregating)Maps and GIS - Scaling DownMaps and GIS - Scaling Down•Large-scale data contains more detail than small-scale data•When using small-scale data (data collected at a small scale) for a purpose that is larger-scale than it was intended for a different kind of problem occurs…Maps and GIS - Scaling DownMaps and GIS - Scaling DownHere we can see a national scale coastline (shown in red) superimposed over local scale data, we can clearly see the generalization and lack of detailIntended useIntended use•Scale of your data must be chosen based on: 1. Your data needs2. The intended use of the existing dataExamplesExamples•Your data options are:–Landsat TM data (30 meter resolution)–SPOT satellite imagery (5 meter resolution)–Ikonos satellite data (1 meter resolution)•What data source do you use when:1. You’re building a nuclear power plant on a site near a lake, and need to plan the location of each component of the plant2. Some illegal cutting of small patches of forest is going on in a national park in the Brazilian Amazon. We want to map where the cuts have occurred throughout the


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