4.4        Metadata

Metadata is information about the data, such as the data source, accuracy, and the dates during which the data are valid. As described below, metadata can be created at several different levels. Per this standard, metadata is required at the collection level when data are submitted. However, the standard accommodates metadata elements at the feature type and feature level. More detailed metadata increases the usefulness and longevity of the data provided. Accordingly, data providers are encouraged to submit metadata at the most detailed level possible.

4.4.1             Collection Level Metadata

Collection level metadata is used to describe a collection of data submitted at one time. A collection may comprise of one or more drawings that contain several layers such as those that make up an ALP, several individual shapefiles that each represent a layer, a single layer stored in a shapefile, or any other combination of allowable data sets.

4.4.2             Feature Type Metadata

Feature type metadata, also known as layer level metadata, is used to describe geometry and attributes for a single layer or feature type. This is the case with metadata that is compliant with the FGDC Content Standard for Digital Geospatial Metadata (CSDGM). This level of metadata applies if different layers within a collection have different metadata.

4.4.3             Feature Level Metadata

Feature level metadata is handled by storing metadata in attributes associated with specific features. All feature classes in the standard carry the following metadata elements (as attributes) for this purpose.

A.      metaId - An identifier used to refer to a metadata record that provides additional information about the data in this record. This is a foreign key link to a database table that can be used to store additional metadata relevant to this feature.

B.      sourceStatement - A statement providing additional details about the source of the data.

C.       editorName - The name of the individual who last edited this data.

D.      lastUpdate - The date upon which any data associated with this record was last updated.

4.4.4             ISO 19915

This standard uses metadata elements defined by the ISO Geographic Information – Metadata Standard (ISO 19115). Of the 409 elements defined in ISO 19115, only 25 are used by this standard, because many of the elements defined in ISO are classified as optional or conditional and do not apply to this standard. Furthermore, some of the mandatory elements in the ISO standard are redundant with the specifications of this standard and are therefore not necessary for data exchange. Table 4-11 lists each metadata element used in this standard along with the level of applicability and provides a description of the metadata elements required per this standard. These elements have been extracted from ISO 19115.

Table 4-11. Metadata Elements Required by MDOT MAA

4.4.5             Temporal Relevance

One of the most critical metadata elements to the aviation industry is time. The frequency with which airport infrastructure changes requires spatial data to possess an indication of the time period for which the data are valid. For example, the existence of a runway may be valid from the time it was authorized for use until further notice. This standard defines the beginning and ending date and time for which each feature instance is valid. All features must have a beginning date (i.e., data are valid until further notice), an ending date (i.e., the data expire at a specified time), or both (i.e., the data are valid only during the period specified). These values are held in the begUsageDateTime and endUsageDateTime metadata elements defined in Figure 4-11.

4.4.6             Accuracy

Accuracy is one metadata element that is particularly important to airport GIS applications. Accuracy is broadly defined as the quality of nearness to the true value. For the exchange of data as specified in this standard, it is important to be more specific. This standard, therefore, provides limits for the absolute horizontal positional accuracy of each feature type. These limits are described as a maximum number of feet between a feature’s actual position and the position indicated in the data provided. The actual position is defined as the feature’s true location on the specified geoid. Since the earth’s surface has many variations, it is approximated by a geoid. The difference between a feature’s true and recorded positions is required at a 95% confidence level. This means that statistically, 95% or more of the features provided fall within the required accuracy limit.

For some feature classes, particularly for FAA required feature classes, vertical accuracy limits are also provided. These accuracies are expressed as the maximum number of feet a feature’s recorded elevation can differ from its actual elevation. Again, the actual elevation is measured from the geoid elevation at that location. Elevations are also to be provided at a 95% confidence level.

Accuracy requirements are driven by the way the data are to be used. The location of an airport on a map used for aircraft navigation must be much more accurate than its location on a national map of airports provided for general information purposes.

The accuracy guidelines provided in this standard have been derived from several sources, including FAA AC 150/5300-18B, RTCA User Requirements for Aerodrome Mapping Information, FGDC Geospatial Positioning Accuracy Standards-Part 4 (sources are indicated in order of precedence). Further information on accuracy definitions and methods to assess the accuracy of existing data can be found in the FGDC Geospatial Positioning Accuracy Standards-Part 3: National Standard for Spatial Data Accuracy (FGDC-STD-007.3-1998).

4.4.7             Security Sensitivity Levels

Sensitivity level is another important metadata element. Because spatial data can be used for nefarious purposes, the data must be protected from unauthorized users. The Code of Federal Regulations (49 CFR Part 1520) defines Sensitive Security Information (SSI) and methods for protecting the information. Protecting sensitive spatial data is therefore not just good practice, it is the law. However, overly protecting data limits the information’s usefulness, in many cases needlessly. The challenge is to restrict data to users having an Uoperational need to knowU and whose credentials the data provider has qualified. Relative to spatial data, this challenge is particularly complex because of the wide variety of data users and ways in which they need to use the data. An efficient way to restrict access to spatial data is to apply specific restrictions at the feature type level. This standard applies one of the following sensitivity levels to each feature type. The sensitivity levels are based on the MDOT MAA Spatial Data Security Standard and conform to the classifications listed in the MD_ClassificationCode list in ISO 19115.

A.      Unclassified data are available for general disclosure.

B.      Restricted data are not available for general disclosure.

C.       Confidential data are available for users that can be trusted with the information.

D.      Secret data are to be kept or intended to be kept private, unknown, or hidden from all but a select group of people.

E.       Top Secret data are of the highest secrecy. At MDOT MAA, this classification is reserved for SSI. MDOT MAA defines SSI as data that depicts the location of Controlled Access Security System (CASS), Closed Circuit Television (CCTV), Flex Response System, and Computer Aided Dispatch (CAD) system and their components. Individuals who require or are provided with this type of information must abide by the requirements of the MDOT MAA PEGS Manual PEGS V2, Chapter 3.1.2 Electronic documents containing Sensitive Security Information (SSI).

Since sensitivity levels are established for each feature type by this standard (See PEGS V1, Appendix 1E.1 Feature Types), it is not necessary to include this information (i.e., a classification code in ISO terminology) in the metadata.