How do the "Source Citation Abbreviation" and "Source Used Citation Abbreviation" work?

The standards establish a set of sources (the "Source Information" element) and set of processes (the "Process Step" element). Usually, many sources and many processes are used to develop a data set of geospatial data. How can the sources and the process steps be linked?

One could describe each source used in the description of each processing step, or describe all the processing steps in which each source participates in the description for the sources. A better way would be to link the source descriptions to the appropriate processing steps. The standards do this through the source abbreviations.

Assign a unique abbreviation to each source. The standards do not describe how to create the abbreviation. One means is to use the Originator and Publication Date of the source. Other styles also are possible. For example, a discipline that had a standard style for citing references in professional papers might choose that style for the abbreviation. Large organizations that have a library of source materials may choose to use the library's unique identifier for each source as the abbreviation. The most important thing is that each source must have a unique abbreviation.

Use the abbreviations to link the sources to the processing steps.

How does the "Source Produced Citation Abbreviation" work?

The "Source Produced Citation Abbreviation" is used when a process generates an intermediate data set that an organization wishes to note separately. To use this feature, the intermediate data set must be documented as a source. It can then be referenced by any processing step.

For example (see figures below), an organization (named Agency A) might compile wetlands information on an orthophoto and then digitize wetlands information. The organization wishes to document the activity using the standard and requires that the compilation and digitizing process steps be described separately. In addition, the organization obtained the orthophoto from another organization (named Company B).

Is source "Company B 1993" the source for the second processing step...?

In the first process step, wetlands are compiled onto the orthophoto (source Company B 1993). In the second step, the wetlands are digitized from the annotated orthophoto. But from what source? One choice is source Company B 1993, although that source (the orthophoto) does not have the compiled wetlands information.

Another choice is to have the first process step produce a "source" which is the annotated orthophoto. This source would be described using the Source Information element, and abbreviated as Agency A 1994. Source Agency A 1994 (the annotated orthophoto) can then be referenced by subsequent process steps.

What does SDTS say about lineage?

Lineage:

The lineage portion of a quality report shall include a description of the source material from which the data were derived and the methods of derivation, including all transformations involved in producing the final digital files. The description shall include the dates of the source material and the dates of ancillary information used for update. The date assigned to a source shall reflect the date that the information corresponds to the ground; however, if this date is not known, then a date of publication may be used, if declared as such.

Any data base created by merging information obtained from distinct sources shall be described in sufficient detail to identify the actual source for each element in the file. In these cases, either a lineage code on each element or a quality overlay (source data index, etc.) shall be required.

The lineage portion shall also include reference to the specific control information used. Control from the National Geodetic Reference System shall be identified according to identifiers in that system, while other points used for control shall be described with sufficient detail to allow recovery.

The lineage portion shall describe the mathematical transformations of coordinates used in each step from the source material to the final product. The locations of any registration points for coordinate transformations shall be given. The methods used to make coordinate transformations shall be documented. To fulfill this standard, it is acceptable to make reference to separate documentation or the coordinate transformation algorithm used, but the specific parameters applied shall be described for the particular case. Documentation of a transformation algorithm shall include the nature of computational steps taken to avoid loss of digits through roundoff and shall include a set of sample computations including numerical values of coefficients to confirm equivalence of transformations. The documentation of a transformation algorithm shall be available on request by a user obtaining digital data even if that user is not licensed to use the particular software.

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