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3/14/06

Correlation of selected FGDC Homeland Security Working Group and FGDC Geologic Data Subcommittee map symbols

The Geologic Data Subcommittee (GDS) has proposed a set of standard map symbols for geologic and related themes.  During the Standards Working Group review of the GDS standard, it was noted that some GDS symbols address the same topic or feature as symbols approved by the Homeland Security Working Group (HSWG).  The GDS was requested to identify those symbols and to provide explanation regarding similarities and differences with the HSWG standard.  This note constitutes the GDS response.

Upon examination of the HSWG and GDS symbolsets, one general observation became clear.  Because the GDS symbols focus on geologic features, there commonly are several detailed GDS symbols per HSWG symbol, probably reflecting differences in focus of data collection and (or) scale of mapping.  The purposes of the HSWG and GDS symbolsets are somewhat different, but the correlation of symbols from one to the other serves the useful purpose of facilitating the exchange of information from the geologist to the Homeland Security community.

1.  Correlation of HSWG Natural Events symbols (see http://www.fgdc.gov/HSWG/ref_pages/Natural_Events_ref.htm) with GDS symbols:

A.

HSWG symbol for Earthquake epicenter (#6) correlates to the seven GDS symbols for earthquake epicenter (see Appendix A, Section 21, specifically, symbols 21.1 through 21.7).  The GDS symbols are for earthquakes of various magnitudes, whereas the HSWG provides a single, generalized symbol of similar appearance.

B.

After Shock (#4) does not directly correlate with a GDS symbol, because GDS does not use a separate symbol for an After Shock, as it is essentially an earthquake – because most scientific observations made by geologists are addressing past events, the distinction between earthquake and aftershock usually cannot be portrayed on a geologic map; however, maps of recent earthquakes might denote the timing of earthquake events with some notation.

C.

Volcanic Eruption (#9) and Volcanic Threat (#10) have some correlation with GDS symbols found in Section 18 (Volcanic Features).  Most of the GDS volcanic symbols address volcanic features that can be mapped – in essence, the standard focuses on the deposits and the results of volcanic activity, whereas the HSWG symbols focus on current or predicted volcanism.  The closest correlation to the HSWG Volcanic Eruption symbol is the GDS’s “Active volcano on small-scale maps” (symbol 18.66); for HSWG Volcanic Threat, see also symbols 18.65 (“Recent volcano on small-scale maps”) and 18.67 (“Inactive volcano on small-scale maps”).  These GDS symbols are intended for use on small-scale maps (i.e., 1:250,000-scale and less detailed).

D.

Landslide (#7) has some correlation with GDS symbols found in Section 17 (Landslide and Mass Wasting Features).  Most of the GDS landslide symbols address features that can be mapped – in essence, the standard focuses on the

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