

DIGITIZN.TXT - 17th of 19 digital documentation files distributed
               with the "Forest Fire Chronology of Saskatchewan"
               (FFCS) dataset.


<Document overview>

     Describes the methods used to digitize the FFCS fire
     boundaries and attributes.


<Background>

     The FFCS dataset was generated using several methods and a
     myriad of source map types.  The methods used for digitizing
     the fire boundaries are categorized by grouping the years of
     the fires:

          (A) 1945 to 1989, excluding 1972 to 1976
          (B) 1972 to 1976
          (C) 1990 to 1994
          (D) 1995 and 1996

     It was initially attempted to only digitize fires that were
     individual polygons at least 1000 ha.  For example if a
     "NO-NAME" fire is based on two non-contiguous areas of 500
     ha each, the 1000 ha minimum is not satisfied.  This rule
     applied more to the 1945-89 dataset than for those in the
     1990s.

     Most of this document describes the burn data digitization
     with these category letters referred to in the text.


<Scale of source maps>

     Fire boundaries were primarily provided on 1:50,000 and
     1:250,000 source maps (categories A and C).  However, burn
     perimeters were also depicted at other scales (1:12,500,
     1:15,840, and 1:unknown).  Fires that occurred in the 1940s,
     1950s and 1960s particularly were provided on a variety of
     source scales.  Most category (B) fires were on a
     1:1,000,000 source map.  Some category (D) fires were on
     1:12,500 forest inventory maps and were digitized off of those
     source maps.  A few category (D) fire boundaries were recorded
     using GPS receivers and thus have no source scale.


<Preparations for digitizing>

     Source map scales were not maintained in the FFCS dataset;
     almost all fire boundaries were transcribed to National
     Topographic Series 1:250,000 (NTS250) basemaps for
     digitizing.  The NTS250 basemaps varied from Series 1 to
     Series 4, depending on the version available.  In most
     cases, the transcribing of burn boundaries to 1:250,000 was
     done visually, but the odd map was ported across using a
     device such as a pantograph.  These preparations pertain to
     category (A) and (C) burns as well as the vast majority of
     (D) fires that were not in the commercial forest.


<Digitization procedures>

     Master burn boundary mylars were coordinated to NTS250
     reference tics.  The tics were in extended UTM Zone 13
     coordinates.  Editing tolerances used were the default
     values.

     Category (A), (B), and (D) fires were digitized according to
     basic manual tracing procedures: wherever a line was
     depicted on the map, that is where the line was digitized.
     Most category (C) fires perimeters were digitized somewhat
     differently.  These fires were digitized using a method that
     would have facilitated achieving perfect vertical
     integration with NTS250 waterbodies, (see DATAISSU.TXT).
     For these fires, the digitizor intentionally strayed into
     the waterbody whenever the fire boundary was shared by the
     land/water interface.  As such, these fires have noticeable
     V-shaped arc segments where the boundary enters a lake.

     Some fires were delineated directly into digital form using
     Global Positioning System (GPS) receivers.  While flying the
     perimeter of a fire, GPS dataloggers tracked the flight
     path.  Note that the flight path may have approximated the
     burn boundary -- it may have followed bulldozer fireguards
     rather than the true boundary.  The GPS boundaries pertain
     to the odd category (D) fires.

     Some fires were digitized at a 1:12,500 scale.  These are
     easily distinguishable from all other burn boundaries in
     that they are surrounded by Arc/INFO georeferencing tics
     that are based on 10 kilometre grids.  Almost all of these
     category (D) fires occurred in the commercial forest and are
     called "project fires" by Forestry Branch.

     For details on how the source data for 1:12,500 category (D)
     fires were collected and how they were digitized, contact
     Forestry Branch.  Details about how the 1:million category
     (B) fires were digitized can also be obtained from Forestry
     Branch.

     Fire boundaries that crossed NTS250 neatlines were
     edgematched and brought into a master year coverage.  (At
     most, the master coverages span the forested region of
     Saskatchewan, at the least they just span the areas burned).
     Fire labels were assigned to every polygon and the
     associated attribute database fields were filled.  Basic
     topology checks (dangles, labelerrors, redundant nodes) were
     performed.  Applies to category (A) and (B) fires.


<Digitization equipment and software>

   - Gentian digitizing tables (models Altek C30 and C31) hooked
     up to a 286 PC with the EM4105 Tektronix 4105 terminal
     emulator package.  (A), (C), and (D)
   - Gentian digitizing tables (models Altek C30 and C31) hooked
     up to Tektronix 4207 terminals.
   - PC-Arc/INFO v.3.4D on a NEC 386.  (A)
   - Arc/INFO v5 on a Prime.  (A)
   - Arc/INFO v6 and v7 on a Sun Sparc Station 10 Model 30. (B)
     and those (C) fires occurring north of the commercial
     forest.
   - Arc/INFO v7 on a Sun 670MP server.  Only those (D) fires in
     the commercial forest.
   - Trimble Pro XL GPS, Basic Plus GPS & CMT Datalogger, CMT-
     GPS.  (D)



This document prepared by:

Ott Naelapea
Wildlife Branch
Saskatchewan Environment & Resource Management
Box 3003, 800 Central Avenue
Prince Albert, SK.  S6V 6G1
CANADA
(306)953-2671 - Tel.
(306)953-2750 - Fax.

November 28, 1996


Revisions:

April 10, 1997
  - added 1996 to category (D) in the <Background> section.
  - added GPS reference to <Scale of source maps> section.
  - noted 1:12,500 and GPS sources for category (D) fires
    in the <Scale of source maps> section.
  - appended (D) reference to GPS equipment list in the
    <Digitization equipment and software> section.
