The projected co-ordinate system transforms information from a three-dimensional Earth surface to a two-dimensional plane, thereby get the better ofing the troubles of mensurating distance between points on a spherical surface ( basic theoretical account of Earth ) , as the unit of informations is ( comparatively ) uniform on a level surface and this enables the measuring of distances and countries between points.
The Earth is non genuinely spherical but instead spheroidal. Different parts of Earth have different data points which are measured otherwise. The locations of data points besides do alter easy over clip due to natural procedures such as motion of tectonic home bases ( Delaney & A ; Van Niel, 2009 ) . Geographic Coordinate Systems are created based on the different data points used. From clip to clip the data point of an country would be re-evaluated and the updated data point values established. Subsequently, new Geographic Coordinate Systems that incorporate the new data points would so be created.
Datum is “a mathematical description of the form of the Earth” ( Delaney & A ; Van Niel, 2009 ) , which is non genuinely spherical but instead spheroidal, with farther deformations caused by influences of the continents. The data point defines the beginning and orientation of latitude and longitude lines, therefore is used as a mention for mensurating locations on the Earth surface ( Beginning: ArcGIS Desktop Help ) .
The geographic co-ordinate systems define locations on a spherical or spheroidal surface ( as the theoretical account of Earth ) and utilize the latitude and longitude values as mentions to a specific location. These latitude and longitude values are given in grades, proceedingss and seconds. Measuring distance utilizing such systems is hard as the values are non changeless particularly along the longitude lines. Each geographic co-ordinate system requires information about a data point, premier acme and angular unit ( Beginning: ArcGIS Desktop Help ) .
The jutting co-ordinate systems define locations on a level surface ( 2-dimensions ) and has similar unit of informations. These systems have changeless lengths, angles and countries and are ever based on a geographic co-ordinate system ( Beginning: ArcGIS Desktop Help ) . However, jutting co-ordinate systems are derived from different types of projections that have different types of associated deformations and advantages. Users are responsible for taking the most suited projected co-ordinate system for their demand while seeking to minimise the accompanied deformations.
We must alter the co-ordinate system of a bed when the co-ordinate system of the bed is different from other beds and we need to analyze the beds together. This is because most GIS package require the beds to hold the same co-ordinate projection and data point before they can be analysed together to avoid comparing informations that are non in the same spacial plane.
Specifying the co-ordinate system:
Frequently a shapefile is provided without any specific information on the type of co-ordinate system used to specify the bed ‘s characteristics. We can look into the handiness of that information under the Shape column ‘s “Spatial Reference” belongingss. If it is stated as “Unknown” or “Assumed Geographic” , so the co-ordinate system of the bed was non decently defined and we can manually make it. If we have the necessary information, we can specify a new co-ordinate system by accessing ArcCatalog under the File bill of fare & gt ; Properties & gt ; XY Coordiinate System check and take the appropriate system ( Beginning: ArcGIS Desktop Help ) .
Entire country of Sclerophyl Woodland and Forest = 1263.43 hour angle, 159 polygons ( spots of woods )
Answer 10: 5 polygons
It omits the route lines outside of the vegetation_94 characteristic category boundary. The properties of the route features in the new route characteristic category are the same as in the old Roads_94 bed, merely the extent of the new route bed is limited by the flora bed boundary.
The ‘Clip‘ characteristic enables users to cut out a piece of one characteristic category ( incorporating lines, polygons or points ) utilizing the characteristics of another characteristic category ( incorporating merely polygons ) as the templet ( Beginning: ArcGIS Desktop Help )
Delaney, J & A ; Van Niel, K. 2009.Geographical Information System: An Introduction ( Second Edition ) . Oxford University Press.
ESRI. 2008. ArcGIS Desktop Help. ArcGIS 9.3 Software. ESRI.