MISALIGNED AND IMPROPERLY REFERENCED DATA IN GIS

THE PROBLEM

When data is projected into a different coordinate system, in addition to distance, area, angles and direction of the map are deformed. To prevent this problem, we should make sure that the downloaded data are aligned and properly referenced. This helps further actions and analyses to run smoother. To do so, we first check to see if the coordinate systems, datum and units of all files are matching. These properties can be found by right-clicking on the file in ArcCatalog then going to ‘properties’. Most of necessary information is under ‘Spatial References’.

HOW TO FIX THE PROBLEM

To fix this problem in GIS, we launch ‘properties’ from ArcCatalog (like explained previously) and under ‘XY Coordinate System’ tab choose the relevant coordinate system and click ‘OK’. However, if spatial analysis needs to be done, the appropriate action is to project a layer. Projecting a layer transforms data and creates a new layer with a different coordinate system. To do this, first we add the file we are working with to Table of Contents. Then launch ArcToolbox from toolbar then navigate to Data Management Tools > Projections and Transformations > Project. A window will pop up. The ‘Input Dataset’ field should be filled with the name of the file and for the ‘Output Dataset’ field find the official/common projection. Finally add the new layer to the map.

WORKING WITH REMOTELY SENSED LANDSAT IMAGERY

Sunlight is used in landsat imagery as the energy source to measure responses of objects and surfaces on earth. These images are not just pictures but contain many layers of data collected along visible and invisible light spectrum. These images are used to look at earth’s surfaces including types of vegetation, water areas and etc. They’re advantageous in a sense that they provide repetitive observations of the Earth since 1972, which allows analysts to compare images of different times and determine changes that are occurring.

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