Download Cartography and Geomatics - GIS and Mapping - Lecture Slides and more Slides Geology in PDF only on Docsity! GEOG205 Select a website related to the course– Cartography + Geomatics, that : > You find helpful in enhancing the course understanding > Covers mapping topics of high interest to you This should not have been previously referred to in class or labs. Docsity.com Google DNA Maps
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Generalisation is needed to simplify reality As SCALE goes down, this increases in all steps Simplification: features lose dimensionality This is called collapsing Examples : > areas to lines: rivers > areas to points: cities > lines to points: ? Docsity.com The process of generalization consists of these three steps: 1. simplification -> 2. selection -> 3. classification (4. -> symbolisation ) Docsity.com 1. Simplification Most features have three dimensions: length, width and height, …. but must lose the third dimension as maps and displays are usually flat. Simplification determines the most important characteristics (dimensions) 3D Volumes (reality) 2D Areas/polygons 1D Lines / arcs 0D Points Docsity.com Selection: example
The following four display panels are labelled with the data's production scale:
1:20 p00 1:50 900 1:260,000 1:1,000,000
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Decreasing Data Capture Seale
Increasing Generalization
All four panels have the same display scale".
“Actual display scale of the figure above depends on your computer monitor size
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How Long Is the Coast of Britain? Unit = 200 km, length = 2400 km Unit = 50 km, Infinite? length = 3400 km Docsity.com Impact of selection with decreasing scale 1:50,000 - air photo (1:25,000) – 1:250,000 Fewer features, fewer details (and fewer named features) e.g. as scale is reduced by 2, # features for the same area might be reduced by ~4 (22) Here scale is reduced by 5 between the 2 maps, so # features is reduced by (in theory)-> Docsity.com
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Summary of scale and generalization There is a practical level of detail associated with any scale. One could identify a 'minimal resolvable unit' of about 0.5 mm. This translates for common scales in metres: 1:20,000 10 1:50,000 25 1:250,000 125 1:1,000,000 500 Data captured at one scale are not transferable to widely different scales: data from a larger scale are too detailed for smaller scales, and data from a small scale are too generalised for larger scales. Online viewers (google maps, mapplace) zoom in through varied scale layers Docsity.com
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