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2. Data Quality


Data Quality provides information on, and a general assessment of, the quality of a data set or information resource. This section contains definitions and examples for the following metadata elements.

Methodology
Collection Instrument Name
Attribute Accuracy
Logical Consistency Report
Completeness Report
Lineage
Positional Accuracy
Cloud Cover

Methodology
Definition: A brief description of specific activities associated with the data collection process. This could include: hypothesis formulation, research design, measurement tactics, and analytic techniques, etc.

Format: Free text.

Example:
Methodology: Data for the National Core and the National Core and Supplement Files were collected annually through 1981 and have been collected every two years since that time. Each household completes a set of core questions about housing expenditures, taxes, insurance, etc., and an additional set of supplement questions that varies from year to year. The metropolitan area data are collected on a continuous basis and are reported annually. Prior to 1984, these data were collected on a sample of approximately 20 SMSAs per year and were called SMSA Files. Since 1984, data have been collected on a rotating sample of 44 MSAs. Eleven MSAs are surveyed each year, with any given MSA surveyed once every four years.

Collection Instrument Name
Definition: The name of the instrument(s) or hardware used to collect the data.

Format: Select from the following list; or free text.
Collection Instrument List: algorithm
questionnaire
human observer


Example:
Collection Instrument Name: human observer

Attribute Accuracy *

Attribute Accuracy provides an assessment of the accuracy of the identification of entities and assignment of attribute values in a data set. This metadata element encompasses the following sub-elements.

Attribute Accuracy Report
*
Definition: An explanation of the accuracy of the identification of the entities and assignments of values in the data set, and a description of the tests used.

Format: Free text.

Example:
Attribute Accuracy: Attribute accuracy is tested by manual comparison of the source with hard copy printouts and/or symbolized display of the digital wetlands data on an interactive computer graphic system. In addition, WAMS software (USFWS-NWI) tests the attributes against a master set of valid wetland attributes.

Quantitative Attribute Accuracy Assessment
A value assigned to summarize the accuracy of the identification of the entities and assignments of attribute values in the data set.

Attribute Accuracy Value
Definition: An estimate of the accuracy of the identification of the entities and assignments of attribute values in the data set.

Format: Free text.
Attribute Accuracy Explanation
Definition: The identification of the test that yielded the attribute accuracy value.

Format: Free text.
Logical Consistency Report *
Definition: An explanation of the fidelity of the relationships in the data set, and the tests used.

Format: Free text.

Example:
Logical Consistency Report: Polygons intersecting the neatline are closed along the border. Segments making up the outer and inner boundaries of a polygon tie end-to-end to completely enclose the area. Line segments are a set of sequentially numbered coordinate pairs. No duplicate features exist nor duplicate points in a data string. Intersecting lines are separated into individual line segments at the point of intersection. Point data are represented by two sets of coordinate pairs, each with the same coordinate values. All nodes are represented by a single coordinate pair which indicates the beginning or end of a line segment. The neatline is generated by connecting the four corners of the digital file, as established during initialization of the digital file. All data crossing the neatline are clipped to the neatline and data within a specified tolerance of the neatline are snapped to the neatline. Tests for logical consistency are performed by WAMS verification software (USFWS-NWI).

Completeness Report *
Definition: Information about omissions, selection criteria, generalization, definitions used, and other rules used to derive the data set.

Format: Free text.

Example:
Completeness Report: All photo-interpretable wetlands are mapped. In the treeless prairies, 1/4 acre wetlands are mapped. In forested areas, small open water and emergent wetlands are mapped. In general, the minimum mapping unit is from 1 to 3 acres depending on the wetland type and the scale and emulsion of the source aerial photography. In regions of the country where evergreen forested wetlands predominate, wetlands smaller than 3 acres may not be mapped. Thus, a detailed on-the-ground and historical analysis of a single site may result in a revision of the wetland boundaries established through photographic interpretation. In addition, some small wetlands and those obscured by dense forest cover may not be included in this data set.

Lineage *

Lineage provides information about the events, parameters, and source data which constructed the data set, and information about the responsible parties. This metadata element encompasses the following sub-elements.

Source Information
*
Provides a list of sources and a short discussion of the information contributed by each.

Source Citation
*

Definition: A citation to a source data set.

Each Source Citation takes the form of a citation. Guidelines and examples for applying the metadata sub-elements for Source Citation are contained in
Section 8 (Citation Information). Multiples are allowed; each Source Citation requires a separate citation record.

Source Scale Denominator
Definition: The denominator of the representative fraction on a map (for example, on a 1:24,000-scale map, the source scale denominator is 24000).

Format: Integer; Source Scale Denominator >1

Example:
Source Scale Denominator: 24000
Type of Source Media
Definition: The medium of the source data set.

Format: Select from the following list; or free text.
Source Media list:
paper
stable-base material
microfiche
microfilm
audiocassette
chart
filmstrip
transparency
videocassette
videodisc
videotape
physical model
computer program
disc
cartridge tape
magnetic tape
online
CD-ROM
electronic bulletin board
electronic mail system
Source Time Period of Content
*
Definition: The time period(s) for which the source data set corresponds.
Guidelines and examples for applying the metadata sub-elements for Source Time Period of Content are contained in Section 9 (Time Period).

Source Currentness Reference
*
Definition: The basis on which the Source Time Period of Content information of the source data set is determined.

Format: Select from list: ground condition, publication date; or free text.

Example:
Source Currentness Reference: Publication date.
Source Citation Abbreviation
Definition: A short-form alias for the source citation.

Format: Free text.

Example:
Source Citation Abbreviation: USGS1
Source Citation Abbreviation: NWR3
Source Contribution
Definition: A brief statement identifying the information contributed by the source to the data set.

Format: Free text.

Example:
Source Contribution: Aerial photo from which wetlands spatial and attribute information are interpreted.
Process Step
*
Information about a single event.

Process description
*
Definition: An explanation of the event and related parameters or tolerances.

Format: Free text.

Example:
Process Description: NWI maps are compiled through manual photointerpretation of NHAP or NAPP aerial photography, supplemented by soil surveys and field checking of wetland photo signatures. Delineated wetland boundaries are manually transferred from interpreted photos to USGS 7.5 minute topographic quadrangle maps and then manually labeled. Quality control steps occur throughout the photointerpretation, map compilation, and map reproduction processes.
Source Used Citation Abbreviation
*
Definition: The Source Citation Abbreviation of a data set used in the processing step.

Format: Free text.
Process Date/Time
*
Definition: The date and time when the event was completed.

Format: Select from list: Unknown, Not Complete; or free text.
Source Produced Citation Abbreviation
*
Definition: The Source Citation Abbreviation of an intermediate data set that is: significant in the opinion of the data producer; is generated in the processing step; and is used in later processing steps.

Format: Free text; Source Citation Abbreviations from the Source Information entries for the data set.
Process Contact
*
Definition: The party responsible for the processing step.
Process Contact requires contact information. Guidelines and examples for applying the metadata sub-elements for Process Contact are contained in Section 10 (Contact Information). Multiples allowed; each Process Contact listed requires a separate contact record.

Positional Accuracy *

Positional Accuracy provides an assessment of the accuracy of the positions of spatial objects. This metadata element encompasses the following sub-elements.

Horizontal Positional Accuracy
An estimate of accuracy of the horizontal positions of the spatial objects.

Horizontal Positional Accuracy Report
Definition: An explanation of the accuracy of the horizontal coordinate measurements and a description of the tests used.

Format: Free text.

Example:
Horizontal Positional Accuracy Report: Accuracy of these digital data (if not digitally revised), is based upon the use of source graphics which are compiled to meet National Map Accuracy Standards. NMAS horizontal accuracy requires that at least 90 percent of points tested are within 0.02 inches of the true position. The digital data are estimated to contain a horizontal positional error of less than or equal to 0.003 inches standard error in the two component directions relative to the source graphic. NMAS vertical accuracy requires that at least 90% of well defined points tested be within one half contour interval of the correct value. Comparison to the graphic source is used as control to assess digital positional accuracy. Cartographic offsets may be present on the graphic source, due to scale and legibility constraints. Digital map elements require edge alignment between data sets. Data along each quadrangle edge are tested against the data set for the adjacent quadrangle; tests check for positional accuracy between data sets within 0.02 inches tolerance. Features with like dimensionality, and with or without like attribution, that are within the tolerance are adjusted by moving the feature equally in both data sets. Features outside the tolerance are not moved. All disconnects are identified by edge matching flags that document the mismatch. These edge matching flags are located in the SDTS AHDR Attribute Primary Module in subfields EDGEWS, EDGEWR, EDGENS, EDGENR, EDGEES, EDGEER, EDGESS, and EDGESR. If the digital data underwent limited update revision, then the data meet at least the class 2 positional accuracy specification in the draft "United States National Cartographic Standards for Spatial Accuracy". If the digital data underwent standard update revision, then the data meet the class 1 positional accuracy specifications. Certain attributes and/or entities, e.g. BEST_ESTIMATE, convey data accuracy information; for details refer to the SDTS Data Dictionary Module.

Horizontal Positional Accuracy Value
Definition: An estimate of the accuracy of the horizontal coordinate measurements in the data set expressed in (ground) meters.

Format: Numeric.
Horizontal Positional Accuracy Explanation
Definition: The identification of the test that yielded the Horizontal Positional Accuracy Value.

Format: Free text.
Vertical Positional Accuracy
An estimate of accuracy of the vertical positions in the data set.

Vertical Positional Accuracy Report
Definition: An explanation of the accuracy of the vertical coordinate measurements and a description of the tests used.

Format: Free Text.
Vertical Positional Accuracy Value
Definition: An estimate of the accuracy of the vertical coordinate measurement in the data set expressed in (ground) meters.

Format: Numeric.
Vertical Positional Accuracy Explanation
Definition: The identification of the test that yielded the Vertical Positional Accuracy Value.

Format: Free text.
Cloud Cover
Definition: The area of a data set obstructed by clouds, expressed as a percentage of the spatial extent.

Format: Integer; 0 <= Cloud Cover <= 100, Unknown



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© 1998. CIESIN.
Revised: March 1998.
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