After looking at all the sources of error, you may be thinking, “Can I ever trust any data ever that I don’t digitize myself (and then scour for errors with a fine toothed comb)?” The answer, fortunately, is yes, which is awesome, since the time and money that would be wasted digitizing already digitized features due to a mistrust of the data quality would be enormous. But how do you know the data is of high quality and was created by a repeatable source? One answer is metadata - the data about data (and the other is acquiring it from a quality source - conveniently the next section of this chapter).
Metadata is the who, what, why, where, and how of data creation and maintenance. Every time a geospatial data layer is created or manipulated, the technician should create or manipulate Metadata the metadata. When a data layer is created, the metadata should be updated with the technician’s name or agency (who), what the purpose of creating the layer was (what), what task is the layer fulfilling (why), where the data is located (where), when the data was made (when), and by what methods the data was created - digitized, edited, or derived from tools (how).
When data has complete and correct metadata, the end users of that data are in a place to make a more informed decision if that particular layer will meet the specific needs of the project. Was the data created during the correct time frame? Was the data created using aerial or satellite imagery? Was the data the result of a tool or a series of tools? Is the data derived or was it actually created? How accurate is the data? Was the creation method in line with what your project might expect? Did the layer’s creator take a painstaking amount of time to digitize a feature or was it the result of a rush job?
8.4.2: Federal Geospatial Data Committee Standards for Metadata
Standardizing the method of recording metadata allows one technician to quickly find the answer to one of the above questions (merely examples). By standardizing the way metadata is recorded, everyone is recording data in the same way, which leads to fulfilled expectations when a technician is looking for and finds an answer. The Federal Geospatial Data Committee (FGDC) was tasked with creating and implementing metadata standards. While they maintain several geospatial metadata standards, including the International Standards Organization (ISO) and the Content Standard for Digital Geospatial Metadata (CSDGM), they have suggested and are assisting government agencies with utilizing the set forth ISO standards. As large quantities of spatial data is created by government agencies, private companies are also following in suit, adhering to these standards.
ArcGIS utilizes several standards of metadata, including the ISO metadata standard in the metadata form, available for editing in the Description tab in ArcCatalog.
|Figure 8.3: Looking at Metadata in ArcCatalog|
|This image shows how to access a layer's metadata (1 - 2) and how to edit the metadata form (3). The metadata standards can be changed from the ArcCatalog Options, found in the customize menu.|