Fixing Misaligned and Improperly Referenced Spatial Data
Coordinate systems give you a frame of reference to locate features and align them with each other. When data is projected into a different coordinate system, the linear unit also changes, along with area, shape and distance. When this occurs, coordinates can be placed in the wrong location, decreasing the accuracy of the map. To ensure this doesn’t happen, we must make sure that the coordinate systems are the same.
For each of the layers, I would right click and select ‘properties.’ I would then click on the ‘source’ tab and scroll down to the ‘Geographic coordinate system’ section. Here, I would check that each layer has a coordinate system and a datum, and if not I would add one to layers that are missing them. It is vital to make sure the coordinate systems and projections are the same for each of the layers to ensure that each of the layers is correctly coordinated with each other, and data will not be incorrectly located. To do this, I would go to the ArcToolbox, click on projections and transformations and then click on define projection. I would then ensure that each of the layers are using the same projections. Secondly, I would review the unit of measurement for each of the layers. The layers must be in the correct order so that you can see all of the data you wish to present. For example, if creating a map showing the major cities in Canada, you must ensure that the layer showing the provinces of Canada are on the bottom, so that major cities can be placed on top and can be seen.
Advantages of Using Remotely Sensed Landsat Data
Using Landsat data is a key tool for geographers to remotely sense how much change has occurred in an area between short 16 day intervals. This allows geographers to analyse how areas have changed for example before and after a natural disaster, such how flooding impacted New Orleans after Hurricane Katrina in 2005. With this data, risk assessment can be done to analyse what defence systems should be in place and planning how to rebuild the city. As this data dates back to 1972, there is a lot of information to be worked with and a vast number of research can be done with this data. This catalogue of data could be used to map the retreat of glaciers from 1972 until the present day. Landsat is particularly useful in generating data of areas which are difficult or impossible to reach, allowing geographers to understand and map these areas. Importantly, as this data is free, it is not only accessible to geographers with a high budget for their research, and it means geographers do not have to travel to these areas to collect the data themselves. Landsat satellites can display infrared and visible light, so we can analyse data which would not be visible to the human eye.