DataFinder Glossary

GIS DataFinder Home

Definitions Pertaining to Data Layers

Data Layer: An individual file; a single layer that can be added to a GIS project. Potentially many data layers make up a single data set. Not all of the library's spatial data holdings have information provided at the individual data layer. Only our best, most frequently used, and most current data is described in such detail.
What is the difference between data sets and data layers (in the GIS DataFinder)?

[Data Layer] Name: The name of a data layer.

[Data Layer] Publication Year: The publication year of a data layer's parent data set.

[Data Layer] Keywords: Thematic keywords used to describe a data layer. If FGDC-compliant metadata is available for the data layer, the keywords used in the metadata were included. If metadata was not available, Davis Library Reference staff assigned descriptive keywords.

[Data Layer] File Format: The file format of the data layer. Examples include shapefile, coverage, CAD drawing, etc.

[Data Layer] Location on Campus AFS: The path name of the data layer on the campus network (AFS). Only UNC-CH Affiliates have access to the campus network (via ONYEN authentication). The root of AFS is often mapped to the J: drive. If this location is listed as N/A, then this data is not available on the network; check the data set's physical location to determine the location of the CD-ROM or DVD.
What is campus AFS?
How do I access spatial data available on campus AFS?

[Data Layer] Source: Source of the data. Examples include government agencies and private companies that publish spatial data.

[Data Layer] Scale: Scale refers to the map scale of the source data used to create the digital data. In the GIS DataFinder, scale is provided as a ratio. Small-scale data (example 1:2,000,000) shows a large area in little detail; large-scale data (example 1:12,000) shows a small area in great detail.

[Data Layer] Spatial Resolution: Spatial Resolution pertains to imagery; the spatial resolution is the size of the individual pixels that makes up the image. For example, an image with 30-meter spatial resolution is made up of many pixels, which are 30 meters x 30 meters in size. As spatial resolution gets smaller, the spatial detail increases.

[Data Layer] Restrictions: Lists the restrictions imposed by license agreements. The licenses for our spatial data may limit who is allowed to use it and in what ways it may be used. Davis Library Reference asks our patrons to honor our license agreements with the companies and agencies that publish spatial data sets. Redistribution of restricted data to unauthorized users is strictly prohibited.

[Data Layer] Date of Content: The date a data layer's content matched ground conditions. This date may differ from the publication date.

[Data Layer] Data Type: Refers to the model used to represent reality; examples include point, line, and polygon.

[Data Layer] Map Units: The units used in the data layer. Examples include, feet, meters, decimal degrees, etc. Map units vary depending on the layer's coordinate system. For example, a data layer that is not projected (or in a geographic coordinate system) has map units in decimal degrees.

[Data Layer] Datum: "A datum provides a frame of reference for measuring locations on the surface of the earth. It defines the origin and orientation of latitude and longitude lines" (ArcGIS Desktop Help). The GIS DataFinder lists the datum for each data layer.

[Data Layer] Projection: "A mathematical formula that transforms feature locations between the earth's curved surface and a map's flat surface. A projected coordinate system includes the information needed to transform locations expressed as latitude and longitude values to x,y coordinates. Projections cause distortions in one or more of these spatial properties: distance, area, shape, and direction" (ArcGIS Desktop Help). The GIS DataFinder lists the projection for each data layer.

[Data Layer] Global Spatial Extent: Lists whether or not a data layer covers the globe. Y means the data layer is global in its spatial extent. N means the data layer is not global in its spatial extent.

[Data Layer] Spatial Extent, Countries/Territories Include: Lists all of the countries/territories included in the spatial extent of the data layer.

[Data Layer] Spatial Extent, States Include: Lists all of the States included in the spatial extent of the data layer.

[Data Layer] Spatial Extent, Counties Include: Lists all of the counties included in the spatial extent of the data layer. This field is only filled in for large-scale data layers (detailed data layers which cover a small geographic area).

[Data Layer] Category(ies): Lists the thematic category(ies) within the GIS DataFinder which best describe each data layer.

[Data Layer] This layer is from the following Data Set: Lists the parent data set for each data layer.

[Data Layer] For Additional Information, see: Provides an Internet address for more information on this data layer or the data set it comes from.

[Data Layer] Notes: Provides additional information that is not contained in any other fields. Examples include known inaccuracies and additional descriptive information.

Definitions Pertaining to Data Sets

Data Set: A data set is a collection of individual spatial data layers. Usually, spatial data is acquired in large sets. There may be as many as 150 individual data layers that make up a data set. All spatial data sets held by the UNC-CH libraries are included in the GIS DataFinder.
What is the difference between data sets and data layers (in the GIS DataFinder)?

[Data Set] Title: The full title of the data set, as provided by the vendor or agency that published the data.

[Data Set] Vendor/Agency: The name of the vendor or government agency that made the data set available.

[Data Set] Publication Year: The year the data set was published.

[Data Set] Source: Refers to the means by which the library acquired the data set; examples include Federal Government, Local Government, Commercial Vendor, Federal Depository Program, Donor, and Education Program.

[Data Set] Media Format(s): Lists the media on which the data set is available. Most of our data is available via CD-ROM or DVD. Our highest quality or most frequently requested data is also available on the campus network (AFS), which is restricted to those who have an ONYEN.

[Data Set] Data Restrictions: Lists the restrictions imposed by license agreements. The licenses for our spatial data may limit who is allowed to use it and in what ways it may be used. Davis Library Reference asks our patrons to honor our license agreements with the companies and agencies that publish spatial data sets. Redistribution of restricted data to unauthorized users is strictly prohibited. Please keep in mind that the license restrictions for some of our data sets vary by data layer.

[Data Set] Physical Location(s): The physical location of the data set (on CD-ROM, DVD or other media) in the library(ies).

[Data Set] Call Number: The call number of the dataset.

[Data Set] For Additional Information, see: An Internet address for more information on this data set.


[Data Set] For Additional Information, see also: A second Internet address for more information on this data layer or the data set it comes from.

[Data Set] For Online Metadata, see: An Internet address for online metadata.

[Data Set] Global Spatial Extent: Lists whether or not the spatial extent of data layers within a data set cover the globe. Y means the data layers are global their spatial extent. N means the data layers are not global in their spatial extent.

[Data Set] Spatial Extent, Countries/Territories Include: Lists all of the Countries/Territories included in the spatial extent of the data set.

[Data Set] Spatial Extent, States Include: Lists all of the States included in the spatial extent of the data set.

[Data Set] Abstract: Provides a description and/or intent of the data set. The abstract is compiled from information obtained from the vendor or government agency that made the data set available.

[Data Set] Keywords: Thematic keywords used to describe a data set. If FGDC-compliant metadata is available for the data layers in a data set, the keywords used in the metadata were included. If metadata was not available, Davis Library Reference staff assigned descriptive keywords.

[Data Set] Notes: Provides additional information that is not contained in any other fields. Examples include known inaccuracies and additional descriptive information.

[Data Set] Contains data layer(s): Lists the data layers contained within a data set.


GIS DataFinder Home

Can't find what you are looking for?
For assistance locating GIS data, please contact:
Amanda C. Henley, GIS Librarian
amanda.henley@unc.edu