Wednesday, May 25, 2011
Tuesday, May 17, 2011
Lab 6 - DEM
The images here demonstrate the Mount Wilson in southern CA. I have chosen it because the whole area is covered by mountains and so it is a perfect territory to show all the DEM tools of ArcGIS. All the forms of demonstration are important and informative, but I think that the 3D model demonstration is the most informative because it really gives you a feeling of the topography of the area.
EXTENT INFO:
Spatial Reference: GCS_North_American_1983
Datum: D_North_American_1983
TOP - 34.33dd
BOTTOM - 34.22dd
LEFT - -118.04dd
RIGHT - -117.83dd
Wednesday, May 11, 2011
Lab 5 - Projections
The first equal area projection that I have presented is the world-cylindrical projection. This is a map projection in which the surface of the globe is depicted as if projected onto a cylinder. A cylindrical projection produces a rectangular map with the equator in the middle and the poles at the top and the bottom. Distortion of the shape and scale is minimal near the equator and is maximal near the poles. The distance between Washington D. C. and Kabul, Afghanistan on this projection is 10200 miles.
My second equal area projection is Bonnie projection. It is named after Rigobert Bonnie after he used it extensively in his 1752 maritime atlas. It is a pseudo-conic projection; the parallels are plotted as concentric, equally spaced arcs. This projection was very popular in the first half of the 20th century, but it lost its popularity in the recent years, because the distortion around the edges limits its use in global maps. The distance between Washington D. C. and Kabul, Afghanistan on this projection is 6590 miles.
The second equidistant projection is the equidistant-conic projection. This projection is very simple to construct and are widely used in regional and national maps of temperate zones. However this projection is not so appropriate for world maps. The equidistant-conic projection has constant parallel spacement, so the scale is the same along all the meridians. The distance between Washington D. C. and Kabul, Afghanistan on this projection is 6950 miles.
The first conformal projection presented here is the World-Mercator projection. On this map all the lines on constant bearing (rhumb lines) that make constant angles with meridians are represented by straight segments. This projection is widely used for navigational purposes at sea. Its 2 properties – conformality and straight rhumb lines make this projection uniquely suited to marine navigation. The distance between Washington D. C. and Kabul, Afghanistan on this projection is 10200 miles.
The second conformal projection is the World-Gall-Stereographic projection. This projection is an improvement upon the Mercator projection. The northern and southern parts of the map are stretched horizontally; while the whole map is stretched vertically. World-Gall-Stereographic projection is mostly suitable to show the temperate countries. The distance between Washington D. C. and Kabul, Afghanistan on this projection is 7268 miles.
As we can see from all these types of projections the shape and scale of the countries, the distance between two locations on Earth is widely dependent on the projection that has been used. This is shown by our lab work – the distance between Washington D. C. and Kabul, Afghanistan ranges between 5066 to 10200 miles on different projections, while the true distance is 7000 miles.
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