Definition of Metadata

Metadata are used to describe data or information. In environmental sciences like oceanography, metadata describe the information that scientists collect and informs users about the characteristics and history of a data set or data item—including methodological, temporal and spatial information.

The word metadata is sometimes used in a singular form (metadata is). We use the plural (metadata are). Both are in common usage, though in the sciences it’s typically used in the plural.
The National Information Standards Organization (NISO) defines metadata as "structured information that describes, explains, locates, or otherwise makes it easier to retrieve, use, or manage an information resource." The World Wide Web Consortium (W3C) defines metadata as "machine understandable information for the web." The Federal Geographic Data Committee (FGDC) defines metadata as describing, "the content, quality, condition, and other characteristics of data." Put simply, metadata are data about data. They provide context for research findings, ideally in a machine-readable format. Once published, metadata can enable discovery of data via electronic interfaces and enable correct use and attribution of your findings.

The results of data collection are generally objects—photos, spreadsheets, maps, graphs, data files, etc. These objects are useful but generally do not contain information about how, where, or by whom the data was collected. The data object alone is difficult to interpret and use. However, if you provide the right descriptive information, your data become much more useful. The additional information might include things like latitude and longitude, date collected, precision of the measurement, person to contact with questions about the data, or type of equipment used. This context, or descriptive data, is the metadata.


The Difference between Metadata and Data

Metadata describe a data set sufficiently to permit searching and using the data. However, it is not always clear if a particular piece of information should be classified as data or metadata. Some information, such as geographic coordinates of observations, can be classified as both data and metadata. The distinction between metadata and data depends on the context and the needs of a given application or user.

Briefly stated, any data that are required to make other data useful or searchable can be called metadata. Again quoting the NISO guide, Understanding Metadata, “Metadata is key to ensuring that resources will survive and continue to be accessible into the future.” To illustrate this important distinction, consider a conductivity-temperature-depth (CTD) profile where a single temperature measurement may be lost without significantly degrading the value of the profile. The loss of positional information from a metadata record, however, renders the data almost useless.


Metadata Structure

Metadata do not have to be in any particular format to qualify as metadata—notes scribbled onto a post-it note and stuck onto your computer monitor can be metadata, though not particularly useful ones. Later guides discuss the importance of machine readability for metadata, and of metadata standards and specifications. Here, we introduce you to the terms commonly used to describe metadata: element and value.

Elements refer to the categories of metadata used. They can also be referred to as properties, or more informally, as fields. Values refer to the actual information filled into an element. Using the above examples, latitude would be an element, and +32.5 might be a value for that element from a particular data record. Similarly, core type would be an element, and piston core and megacore would be values for that property.  


Examples of Metadata

Television programming provides a simple example of metadata. When you turn on a television and want information about the next show, you will probably go to an index of television shows. You may consult the TV listings in a newspaper or in TV Guide, or you may view on-screen program information. The listings you look at contain data (show title, type of show, time, or plot summary) about other data (the television broadcasts themselves).

Scientific examples are more complex, but the same concept applies. The notes written by scientists about their experiments—in lab notebooks, log books, or other documents—are metadata (information) about data (the results of the experiment). The notes describe characteristics of the experiment.


Oceanographic examples

Data: Photo of a newly discovered species of fish
Metadata: Location of discovery (latitude, longitude, and depth), other fish in the area, salinity of the water, quantity discovered (school, single fish, two or three individuals), etc.
Data: Meteorological Measurements
Metadata: Location of readings (latitude, longitude, and height), instrumentation used to collect data, units, processing done to measurements
Data: Sediment Core Record
Metadata: Location of discovery (latitude, longitude and depth), description of stratigraphy, length, type of coring device


Notice that different types of data require different types of descriptive information. However, there are some standard fields that should always be included (for example, location and date collected).

Suggested Citation

Graybeal, J., Neiswender, C., Stocks, K., Bermudez, L., Galbraith, N., Watson, S., Miller, S.P. 2018. "Definition of Metadata." In The MMI Guides: Navigating the World of Marine Metadata. Accessed October 20, 2020.