GUIDELINES AND RECOMMENDATIONS FROM A MEETING OF THE VENUS GEOLOGICAL
MAPPING STEERING GROUP, WASHINGTON, DC, OCTOBER 24, 1995.

NOTE:  Mappers are referred to the guidelines distributed after the
meeting in Flagstaff during July, 1995.  Those guidelines are not repeated
here.

I. Mapping standards.
   A. Volcanic features.
      1. Pits and calderas.
         a. If D>20 km, use the closed hachured line shown on the USGS
            list of symbols distributed to all mappers.
         b. Use a circle with a central dot for 10km<D<20km.
         c. In general, we recommend not showing pits and calderas with
            D<10km, but if there is a good reason to do so, smaller pits
            and caldera can be shown simply with a dot.
      2. Domes and shields.
         a. use a plus (+) sign for 10km<D<20km (or 5km<D<20km if
            justified).
         b. For domes and shields between D=20 km and D=40 or 50 km:
            1) If the feature has a cone- or shield-shaped profile, use a
               plus (+) enclosed in a circle or oval.
            2) If the feature is pancake-shaped (steep-sided dome), use a
               circle or oval with outward pointing barbs in each of the
               4 cardinal directions (like a plus sign with its center
               covered by a circle or oval).
         c. Domes and shields larger than D=40 or 50 km should be mapped
            as separate stratigraphic units.
      3. A graphics file illustrating these volcanic map symbols is
         available in .gif format as map_sym.gif, and can be obtained via
         anonymous ftp from: 128.119.45.20, /pub/mcgill.
   B. Impact craters
      1. It is OK to map just two impact-crater units:
         a. Outflow deposits (the direction of flow can be indicated with
            an arrow, if desired).  Do not use scarp symbol to show
            outflow deposits.
         b. All other deposits (ejecta, rim, floor, central peak),
            undifferentiated.
      2. If desired, peak, floor, rim, and ejecta may be mapped separately
         for very large craters.  However, the central peak should never
         be delineated with a special symbol (to avoid possible confusion
         with volcanic features).
      3. The stratigraphic position (or range of possible positions) for
         each crater should be indicated in one or more of 3 possible
         ways:
         1) as separate range boxes on the correlation chart; craters with
            identical age ranges should be lumped within a single box.
         2) as a text table.
         3) in a text paragraph.
   C. Structures
      1. Be sure that lines used to represent faults, lineaments, etc. are
         drafted with a heavier line than contacts.
      2. The presence of coronae should be indicated by increasing the
         density of the lines used to represent fractures or ridges; a
         specific line completely encircling the feature should not be
         used.  Coronae as structures should not be mapped as material
         units.  However, it is common for portions of coronae to consist
         of mappable units distinct from surrounding plains.
      3. Map only those structures that are distinct on the SAR base.
         Vague structures and topography should not be mapped.
   D. Stratigraphy
      1. Local vs. regional vs. global units.
         a. Widespread plains units.
            1) We must avoid any naming scheme that implies a common age
               or origin for widely separated plains of similar
               appearance.  Plains units may prove to be correlatable
               globally, but this has yet to be demonstrated by anyone.
            2) The most workable scheme is probably to correlate
               regionally; that is, all quadrangles including parts of a
               given planitia should logically have correlatable regional
               plains units.  Thus mappers will attempt to define common
               units on a regional basis.
            3) The names used for these regional plains units should
               convey geographical information; thus vph might stand for
               Vinmara homogeneous plains, tph for Tinatin homogeneous
               plains.  These units should have similar SAR properties,
               but correlation will be left open to explicit
               interpretation.
            4) Mappable members of these regional plains units may be
               identified with names or letters, but not numbers (numbers
               carry undesirable cryptic implications for global
               chronology).  Members can be local to a single quadrangle,
               or of more regional import.
            5) The mapping meeting next summer will include a large block
               of time during which mappers will meet in regional groups
               to settle on common regional plains units, and suggest
               names for these units.  HOWEVER, authors should submit
               their maps to the USGS for review whenever they are ready;
               that is, do NOT wait until after the meeting next summer.
               There will be plenty of time to change unit names before
               the revised maps go to press.
         b. Names of local units should include the source feature
            wherever this can be clearly defined.  Thus hf might represent
            flows emanating from Heng-O.  For such units, members may (and
            commonly should) be numbered.  Thus gf1 and gf2 would
            represent two flow units from Gula Mons that are of
            demonstrably different age.  It also is permissible to create
            generic local units, such as sf for flows emanating from
            shield fields, or cf for flows emanating from coronae.  The
            choice will depend on a balance between added information on
            one hand, and an excess of basically similar units on the
            other hand.
         c. If no source is obvious for a local unit, it should be given
            a simple descriptive name.
         d. Please note that all letters in the symbolic names are lower
            case; use of upper case for the first letter is reserved for
            formal time-stratigraphic terms, and these do not exist for
            Venus at this time.
      2. "Basement"
         a. Great care should be exercised with respect to the age of old
            units.
            1) Even if the materials within tessera terrain appear to be
               the oldest unit in a quadrangle, this in no way implies
               that they are the same age as materials of tessera terrain
               found elsewhere on the planet (remember the 19th century
               error in assuming that metamorphic "basement" on Earth was
               everywhere the same age!).
            2) Many quadrangles have more than one type of material
               occurring as inliers in regional plains.  It is a natural
               tendency to assume that the most deformed of these are
               older than the less deformed (e.g., tessera vs. densely
               fracture plains of some mappers).  Unless the two units are
               actually in contact so that this age relationship is
               demonstrable, the correlation chart should convey the
               possibility of age overlap.
         b. In summary, the correlation chart and the text should indicate
            relative ages based only on explicit evidence in the
            quadrangle or in neighboring quadrangles.
      3. Descriptive names for material units
         a. In general, use English rather than Latin words.  Thus "plains
            materials" rather than "planitia materials", "flow materials"
            rather than "fluctus materials".  "Corona materials" is OK.
            There still is no consensus concerning tessera vs. complex
            ridged terrain.  The problem is that the materials within
            tessera are not everywhere ridged, nor are they necessarily
            complex.  We need a new, strictly descriptive English name for
            the materials of tessera terrain.  For now, "tessera
            materials" will be accepted as an exception to the "use
            English" rule, but this may change.
         b. Descriptive terms such as rough and smooth are preferable to
            bright and dark, because the relative brightnesses of surfaces
            with different roughnesses change with SAR incidence angle.
         c. Pattern (or "textural") terms such as mottled, homogeneous,
            grainy, etc. should be used if appropriate.  Beware of using
            "smooth" where homogeneous is meant; a uniform SAR backscatter
            could derive from a uniformly rough surface as well as a
            uniformly smooth surface.
         d. If possible, avoid using topographic or structural
            characteristics in the name of a unit because these are
            secondary and thus not necessarily related to the materials of
            the unit (Normanskill Formation is Normanskill Formation
            whether exposed on a mountain or in a valley, whether
            horizontal or folded).  Use geomorphic rather than genetic
            terms (e.g., "lineated" instead of "fractured").  We realize
            that it may well be necessary to violate this guideline in
            specific and very difficult cases, but these should be rare.
      4. Radar properties
         a. The radar properties of all regionally important units (such
            as widespread plains) should be included in a table, and the
            backscatter values shown on a graph.
         b. Local units may be illustrated with selected examples.  For
            example, if flow units of similar appearance are mapped around
            several volcanoes, include only a representative sample that
            illustrates the range of backscatter values.
         c. The logic behind the sizes of the sampling boxes should be
            stated, either in the table caption or in the text.

II. Text and Figures
   A. Standard text: members of the Steering Group are writing brief
      paragraphs covering two important topics: 1) a description of the
      Magellan spacecraft and mission, and 2) the basic methodology of
      mapping using SAR images and ancillary data.  These paragraphs will
      be printed as part of the marginal information on all Venus
      geological maps.  Authors must still discuss the specifics relevant
      to their quadrangles in their text (what data cycles, the range of
      incidence angles, how units are defined, etc.), but it will not be
      necessary to discuss these issues generically.  When these
      paragraphs are completed, copies will be circulated to all mappers.
   B. Authors should consult planetary geological maps recently published
      by the USGS for examples of how to organize the text.  There is no
      rigid format, but most text organizations should not deviate in a
      major way from the following model outline:
      1. INTRODUCTION:  covers such topics as the location and size of the
         area, topographic features, and the data products used.
      2. MAPPING TECHNIQUES:  includes problems encountered in mapping.
      3. GENERAL GEOLOGY:  includes regional setting.
      4. STRATIGRAPHY
      5. STRUCTURE
      6. IMPACT CRATERS
      7. SURFICIAL MATERIALS
      8. DISCUSSION; GEOLOGICAL HISTORY
      9. Acknowledgements

III. Reviews
   A. When maps are submitted, the USGS conducts a "pre-review" to verify
      if the author has submitted all of the materials required for the
      scientific reviews.  An incomplete submission can lead to a delayed
      review.
   B. Reviewers receive a USGS "flow sheet".  If a reviewer signs this
      sheet, she/he is stating that the map and text require only minor
      revision, and thus do not need to be subjected to any additional
      scientific review (similar to when a reviewer of a journal article
      indicates that author responses to the review can be evaluated by
      the editor only).  If the map or text requires more extensive
      revision, reviewers should initial rather than sign the flow sheet.
   C. The author check list provided by the USGS is quite explicit about
      what should be submitted.  However, some additional guidelines are
      needed to be sure that the reviewers can do a thorough job without
      unnecessary extra effort.
      1. The 1:5M base mosaic should be submitted with the map because the
         primary reviewer must check every contact against the base.  This
         mosaic will be returned to the author.
      2. The colored and uncolored copies of the geological map should be
         at the same scale as the 1:5M base mosaic.
      3. Depending on who the reviewers are, it may be necessary for the
         author to submit the F_MAPS covering the quadrangle as well.
         This should be negotiated with the USGS mapping coordinator
         (currently Ken Tanaka).  These will be returned to the author.