At the April OGC Technical Committee meetings in Ottawa, the OGC members had a lively discussion regarding the approval of "KML 2.1 - An OGC Best Practice" for release as an official OGC member approved document. The discussion focused on two primary topics: "How does KML relate with the existing OGC Standards Baseline" and "What is the roadmap and process for harmonizing certain KML elements, such as geometry, with relevent OGC and ISO standards". These discussion led to a decision that a short document, or preamble, needed to be developed to address these questions and that would be inserted into the "KML 2.1 - An OGC Best Practice" document. A number of OGC members working with Google staff have developed this preamble document. Following is the preamble:

Preamble "KML 2.1 - An OGC Best Practice"

Google submitted KML (formerly Keyhole Markup Language) to the Open Geospatial Consortium (OGC) to be evolved within the OGC consensus process with the following goal: KML Version 3.0 will be an adopted OpenGIS implementation specification that will have been harmonized with relevant OpenGIS specifications that comprise the OGC standards baseline. There are four objectives for this standards work:

• That there be one international standard language for expressing geographic annotation and visualization on existing or future web-based online maps (2d) and earth browsers (3d).
• That KML be aligned with international best practices and standards, thereby enabling greater uptake and interoperability of earth browser implementations.
• That the OGC and Google will work collaboratively to insure that the KML implementer community is properly engaged in the process and that the KML community is kept informed of progress and issues.
• That the OGC process will be used to insure proper life-cycle management of the KML candidate specification, including such issues as backwards compatibility.

The OGC has developed a broad Standards Baseline. Google and the OGC believe that having KML fit within that family will encourage broader implementation and greater interoperability and sharing of earth browser content and context.

What information sharing space is KML targeted at? KML is an XML language focused on geographic visualization, including annotation of maps and images.  Geographic visualization includes not only the presentation of graphical data on the globe, but also the control of the user’s navigation in the sense of where to go and where to look.

From this perspective, KML is complementary to most of the existing OGC specifications including key standards such as GML (Geography Markup Language), WFS (Web Feature Service) and WMS (Web Map Service).   Currently, KML (v2.1) utilizes certain geometry elements derived from GML (version 2.1.2). These elements include point, line-string, linear-ring, and polygon.

The OGC and Google have agreed that there can be additional harmonization of KML with GML (e.g. to use the same geometry representation) in the future.  The Mass Market Geo Working Group in the OGC will define additional harmonization activities. Other OGC specifications such as Context and SLD will be considered.

Google submitted the KML Reference Manual to the OGC. OGC staff put the reference document into the OGC Document Template. During the April Technical Committee meetings, the OGC membership approved release of the document as an OGC Best Practices Paper. This document is based entirely on the current KML 2.1 reference documentation from Google. This OGC Best Practices document is provided to the community to initiate the process of KML standardization within the OGC consensus process.