Coordinate Systems and Spatial Data Models

How to fix misaligned and improperly referenced spatial data

When data is projected onto a different coordinate system, it can cause distortions. As a result, different types of data must be compromised or distorted in order to preserve another type of data. It can change the shape of an area, like changing the shape of the poles. Most maps are often altered views of the earth’s surface, distorting a round area on a flat surface. As the surface is round, a lot of the information on the area needs to be compressed in order to fit onto the flat surface. Various types of map projections can be used for different purposes.

There are different types of projections – Conformal, equal area, equidistant, and true-direction projections. A conformal projection would maintain angles describing spatial relationships, to preserve local shape. An equal area projection would preserve the area of features shown, by distorting other properties like shape, angle, and scale. An equidistant projection would preserve distances between certain points, and this is maintained by distorting scale. True direction projections maintain great circle arcs, the shortest route between two points.

Projection on the fly process requires fewer steps, and is useful if the type of projection the layer needs to be changed into is known. If the projection is not known, it requires additional research to find it in the metadata or attaining it from the provider.

Projecting a layer using ArcToolBox project and Transformation commands require more steps, but it involves actually changes the data to create a new version. This requires typing in information like the input dataset, output dataset, and choosing the output coordinate system. When typing in the output dataset, one must type in the location correctly in order to easily find it under folder connections in the catalog box.

Advantages of Using Remotely Sensed Landsat Data for Geographic Analysis

Although mixed pixels can be effective in showing an area, as well as the area of a road, it is highly dependent on the pixel size in comparison to the scale of object on the map. A pixel shows an average of one segment of an area – so if an area is mostly deciduous forest, then the pixel will show it as deciduous forest. However, in real life, the land in that particular area is probably mixed with other types of land cover. Therefore, when representing the road, it may not be completely accurate as some areas of the road may not be represented and be represented as other types of land cover instead.