5.4 What Other Kind of Information Do You Need to Use GIS Data?

Once you have your geospatial and attribute data within the GIS, there’s one more important piece of data you’re going to need—descriptive information about your data. When creating data or obtaining it from another source, you should have access to a separate file (usually a “readme” text file or an XML document) that fully describes the dataset. Useful things to know would be information about the coordinate system, projection, and datum of the data, when the data was created, what sources were used to create it, how accurate the data is, and what each one of the attributes represents. All of this kind of information (and more) is going to be critical to understanding the data to properly use it in GIS. For instance, if you have to reproject the data, you’re going to have to know what projection it was originally in, or if you’re going to be mapping certain attributes, then you’ll have to know what each one of those strangely named fields in the attribute table actually represents. In GIS, this “data about your data” is referred to as metadata.

The Federal Geographic Data Committee (FGDC) has developed some standards for the content and format that metadata should have. These include:

• Identification of the dataset (a description of the data)
• Data quality (information about the accuracy of the data)
• Spatial data organization information (how the data is represented—whether it’s vector or raster, for instance)
• Spatial reference information (the coordinate system, datum, and projection used)
• Entity and attribute information (what each of the attributes means)
• Distribution information (how you can obtain this data)
• Metadata reference information (how current the metadata is)
• Citation information (if you want to cite this data, how it should be done)
• Time period information (what dates the data covers)
• Contact information (whom to get in touch with for further information)