Coordinate Systems and Spatial Data Models
Fixing misaligned and improperly referenced spatial data
Projecting data into a different coordinate system causes distortions not only in distance but also shape, area and direction of the data.for general audience. The way in which one would go about fixing distortions following a projection is as follows:
- Preview the data in ArcCatalog in order to be able to identify which data layer if suffering from distortions
- Under the XY coordinate system tab in layer properties, verify the coordinate system, projection and datum (under properties). All these properties must be consistent throughout all layers.
- The data can be projected in the appropriate coordinate system.The projection can be changed either using projecting-on-he-fly or ArcToolbox Project and Transformation Commands in ArcMap.
The projection-‐on-‐the-‐fly process is very practical feature program to align spatial coordinate systems for display and mapping. This is ideal for printing a map that requires a different look than the original dataset. It is far more straightforward and convenient to execute. The Transformation Commands modify the data and create a new version of the data layer with a different coordinate system. This process is ideal when performing spatial analysis as it can be used to change the projection of layers so that they have a common spatial reference system.
Advantages for using Landsat Data for Geographic Analysis
There are many advantages to using remotely sensed Landsat data for geographic analysis. Remote sensing can capture changes in the landscape overtime which can then be used to analyse the impacts processes have had on the environment. An example of this may be: analysis of urban development, in particularly the growth of cities.
Lagos, Nigeria has been titled the “Big Apple of Africa” for its rapid population growth thus it would be interesting to investigate what effect the population growth has had on the urban development of the city and in particular its shape and size. Lagos has enjoyed tremendous growth, reaching 21 million from just 1.4 million as recently as 1970 thus it would be interesting to investigate the change over a 40 year period from 1976 to 2016.
Remotely sensed Landsat data allows us to survey areas which may be inaccessible and is also considerably more cost efficient.
Accomplish Statement
Gained knowledge into the function of ArcCatalog and how to use the program effectively to ensure data is projected correctly. Now able to distinguish the difference between vector and raster data to be able to manage both accordingly. Has also gained experience in working with remote sensing imagery to be able to create a composite image using the different bands from remotely sensed data.