DEALING WITH MISALIGNED AND IMPROPERLY REFERENCED DATA
Different projections preserve different properties (i.e. Mercator preserves angles and directions, Albers Equal Area preserves areas, Lamberts Conformal Conic preserves angles, etc.); thus, when data is projected onto different coordinate systems properties become distorted. When you want to combine different layers of data that are improperly referenced or misaligned you would go into “Properties” in ArcCatalog under the “XY Coordinate System” tab and choose the most appropriate coordinate system. If you need to preform spatial analysis, it is better to change the projection of the layer to a common spatial reference system, which creates a new data layer with a different coordinate system. To do so, you go into ArcToolbox, find Data Management Tools > Projections and Transformations > Project. Input Dataset should be the layer you wish to project and output coordinate system should be the common coordinate system.
USE OF LANDSAT
Landsat is a remote sensing technique used to measure the response of objects and surfaces on the earth. This includes vegetation distribution, land use change, water features, etc. The advantage of Landsat is that observations have been taken since 1972, which provides us with multiple images in different time frames so we can figure out the types of changes taking place. Landsat was especially useful after the Mt. St. Helens earthquake and eruption in 1980 to determine how the surrounding landscape changed.