In this article we will discuss various concepts related to metadata. At the end of this article, you will be able to answer questions such as, what is metadata, its components, importance and role in GIS etc.
Definition of Metadata:
Metadata is most popularly defined as data about data. In GIS, it is called as geospatial metadata.
It describes various details related to map, GIS files, imagery. It consists information such as date of acquisition, methodology adopted for acquiring data, scale, people involved, precision etc.
This is one of the important component of spatial data in GIS, however it is not much attention is paid by many of the GIS analysts.
How Metadata is Used in GIS?
This section describes the importance of metadata in GIS.
- Metadata is similar to catalogue in library. It indexes locations of various items in the database. Using it, it is possible to identify where to look for a particular detail or information in a distributed database of GIS.
- It may also contain information related to precision of data, preparation of data etc. This helps in determining whether a data set can be used for the application or not. A data set may or not be used in a application, depending on what is the precision of data set, how data set is prepared or collected etc.
- Some times depending on data set, it often contains details such as how much relevant data is present in the imagery or data set. This again helps in deciding whether a data set can be used or not. For example, metadata of satellite imagery contain information about cloud cover, if very high cloud cover is present it may not be suitable for usage in a particular application.
- Metadata also contains information regarding data format, technical specifications etc. This helps in identifying the suitable tools and techniques to work with a particular data set.
Who sets standards for Metadata?
Federal Geographic Data Committee (FGDC) of USA, and professional bodies such as International Organization for Standards (ISO) frames certain guidelines for preparing geospatial metadata.
Some of the standards include, Content Standard for Digital Geospatial Metadata (CSDGM) prepared by FGDC, and the North American Profile of ISO 19115:2003 – Geographic information – Metadata (NAP), and the European INSPIRE Metadata Directive etc.
These standards specify guidelines about what are different components of metadata, and how to represent and store the information.
What are the Components of Metadata?
As per FGDC guidelines following components have to be present in the data.
- Metadata record information: It contains information about the language in which metadata is recorded, a unique file identifier for the record and contact person etc.
- Identification information: This includes details of data, that help us in citation such as name, abstract, purpose for creation etc.
- Constraints information – this includes security aspects in using the data, data policies etc.
- Maintenance information – details about frequency of updates and maintenance of data are given.
- Reference system information – indicates types spatial referencing system adopted for creating data sets.
- Symbology information – provides details about different types of symbols used in the maps creation and their meaning.
The above quoted things are some of the important things which a metadata file is supposed to have. However, many of the above things are not often present, and certain things which are not quoted may present in the file depending on the application and data set collected.
The metadata should not create any ambiguity and must help a user in deciding whether a data set can be used or not.
More guidelines and polices related to metadata are being framed and updated to suit the current requirements and improvement. These days FGDC is trying to integrate the standards with ISO to create a better framework for preparing metadata.
One can learn more developments about these developments at FGDC portal.