Overview
The objectives of this module are: - get familiar with spatial data types - understand what a projection is - recognize the difference between raster and vector data - understand basics of scale, resolution and scope
Is Spatial Special?
There have been numerous discussions about the nature of spatial data and whether or not there is anything special about spatial information. Since the Open Geospatial Consortium(OGC) created the Simple Features for SQL specification in 1999, spatial data can be stored alongside other data types as just another column in a table. However,if you look for it, you can see a lot of GIS professionals evangelizing the difference between spatial data and regular data. Is there really a valid reason that spatial data is more unique than temporal or text data types? Is it just GIS professionals trying to sell their expertise as a separate field?
Do they have a point?
There are definitely a few elements that set spatial data apart from other data types. One of the first differences is that spatial data comes in a variety of data types, which are each inter-related. Spatial data is also dependent on a few factors such as projection, ellipsoid, and unit of measure. Spatial data is naturally multi-dimensional but needs to normally be passed through a visualization application to understand. Finally, a sticking point for spatial data has been how should the data be organized effectively and how can the inherent relationships between objects be tested efficiently.
The specification helps to define a few words useful when dealing with spatial data.
A feature is an abstraction of real world phenomena.
The simple features for SQL defined a simple feature as a feature with all geometric attributes described piecewise by straight line or planar interpolation between sets of points.
Rasters and Vectors
There are two main families of spatial data which are each used for a specific function. Vector data, which represents discrete phenomena such as bus stations, and Raster data which represents continuous phenomena like temperature.