Properly Referencing Spatial Data 

Improperly referenced spatial data causes difficulty when data layers do not line up. To prevent this problem, it is always in good habit to visit ArcCatalog and right click each data layer to review the data properties before adding layers to Table of Contents for their display. You can review how the spatial data is referenced by examining right- clicking the data layer and selecting Properties. After the dialog box appears, the Spatial Referencing section can be found by scrolling down under the Source tab. This section provides important information such as the coordinate system, the datum, and the unit of measurement, which enables the GIS user to locate the data according to its proper geographic location on earth.

Often, different data layers contain different coordinate systems, depending on their features. This is usually not a problem, unless you have spatial information missing. However, an error box arises when the coordinate system of a particular data layer is unknown and you try to add the layer to the map. You would have to fix this manually to avoid misaligned data. First, it is essential that the Status Bar option under the View menu is checked. By right- clicking the data frame (the Group under which all the data layers are listed in Table of Contents), selecting Properties and finding the General tab, you can manually select the coordinate system. That way the features of the data layer can be located properly. If this error occurs again with another layer, it would be wise to review the metadata of the dataset, which can be found under ArcCatalog in the Description tab, for additional information or even contact the data provider for better data.

For geographic analysis, it is more convenient for data to be aligned under one coordinate system. Other ArcMap features, such as projection-on-the-fly, are useful. Projection-on-the-fly combines layers in different coordinate systems so they appear to align with one another, without requiring a change in the coordinate system. If you have most of the data layers for the map listed in NAD_1983 coordinate system, a geographic coordinate system, but one data layer referenced as Canada_Lambert_Conic, a projected coordinate system, you could delete the layer with the coordinate system that doesn’t match, in this case the projected coordinate system, find that layer and change its properties under ArcCatalog, so it is in NAD_1983 like the other layers. Then re-add the layer to the map.

Remote Sensing using Landsat Data in Geographic Analysis 

Both remote sensing using Landsat and ArcGIS are useful for geographic analysis. However, when working with land use changes for resource management applications, rather than for planning and engineering applications in urban environments, Landsat data is very useful. Landsat is very applicable for monitoring large-scale geographic changes in the landscape. For example, it can display changes in the landscape (shoreline) before and after a volcanic disaster, changes in forest cover over a certain time interval, or indicate glacial melt through a receding shore line. This is because Landsat uses raster data, which makes it easier to visualize change. Data comes in the form of continuous data (mapped in contour form), such as precipitation, elevation, and land cover, rather than discrete features, such as individual lakes, road networks, and streets, which are displayed as vector data. You can monitor changes in a patterns over particular time intervals or see before and after effects to understand environmental change.