The basic recording unit of raster data is a number of regular grid cells, which can be regarded as a picture element or pixel storing is a form of matrix. It is similar to digital image. Therefore, raster cells are well-suit in a GIS system particularly in representing traditional geographic phenomena that vary continuously over space such as elevation, slope, precipitation, and can also be used to represent humanistic types of data like population density, consumer behavior, and other demographic characteristics.

It is useful in generating information for spatial analysis and modeling, presenting trends such as hydrologic modeling or the dynamics of population change over time. However, only one characteristic of the earth surface is presented on one layer, and is emphasized on the processing of geographical data. Therefore, raster data when used in GIS, the map layers created is preferred in terms of the spatially-registered characteristic.

But for the vector system, data is presented precisely by the basic element-- point, which is regarded as discrete object. Each point is assigned an identification number, the attribute at each point is recorded according to the point's ID number in separate file. However, in a spatial analysis processing of data should based on topological relationship rather than coordinates, there is a need to construct complex spatial objects from the basic element. The built geographical data file and the attribute data file are linked together through the georelational data model. The result is a coverage, or a digital representation of a single map layer exhibiting only one type of map feature.

Performing spatial analysis in vector system is much more complex than in raster system. On the other hand, raster GIS database is much simpler because the topology is already built-in with the grid cell arrangement, and the attribute is an integrated part of the spatial.

In exercise 1, we need to convert the land parcels in shape file and union it with the existing features, after the restructuring we can then perform a spatial query. First transform data to a commonly accepted terrestrial coordinate system such as the Universal Transverse Mercator Coordinate System, so that the two coverage could locate point data exactly. Then to specify and adjust map projection. Another use of coordinate transformations in vector GIS is edge matching, which allows two adjacent maps to be joined.

After the overlay, the topology of the combined coverage created from the overlay operation will have to be updated. The resulting attribute table for the new coverage consists of the old and new attributes formed by logical or mathematical operation on the old ones, and these coordinates need to be resolved. But in exercise 2, we can directly perform the spatial query to meet different conditions.