File Description:

Projection: Albers equal-area, nad 83 datum. May 12, 2005. File originally created by:

Chris Ens,Spatial Information Analyst
Land Information BC
Ministry of Sustainable Resource Management
1259 Dalhousie Dr., Kamloops, B.C V2C 5Z5
Ph: (250) 371-5244  Fax: (250) 371-5293
Chris.Ens@gov.bc.ca

Source Data - 1998 Overview Survey Data, obtained on CD from:
Leo Rankin, Forest Entomologist
Ministry of Forests
Williams Lake, BC

Source Data format: data was in .dgn format, UTM projection, unknown map datum (suspected that there was a mix of NAD 27 and NAD 83 data, depending on the mapsheet).
A separate .dgn file existed for each BCGS mapsheet number within the old Cariboo Forest Region. No forest health-specific attributes were attached to attribute tables (fhf, severity, number of trees, etc) - these attributes were only contained within the text nodes for each feature. All features were polygons - no differentiation was made between polygon infestation and spot infestation. All features had the attributes of FHF, hectares, and either a number of trees, or a % attack.

Data was rolled up into a single file, converted to ESRI shapefile format, and reprojected to Albers Equal Area, NAD 83. All attributes contained in the attribute tables and in the text nodes associated with each feature were included in the final attribute table.

Methodology for assigning severity and spot/polygon attributes to 1996, 1997 and 1998 Cariboo Region overview survey data:
process performed by 
Kevin Buxton, Forest Health Technician
Southern Interior Forest Region
Kamloops, BC
May 12, 2005


Each record was originally assigned either a percent attack, or a number of trees, and an area in hectares. Ordinarily, all records with a percent attack would be called a polygon infestation, and records with a number of trees would be called spot infestations. BUT - in these files, many poygons that were given a number of trees but no severity were of a substantial size (many hectares) and thus did not fit the above protocol well; the opposite was also a common accurrence. Therefore, the following process was used to assign spot/polygon attributes, and to calculate percent attack and resulting severity levels for all records:


1. Assign any records of over 2.0 ha in size to be a polygon ("n" under the spot attribute).

2. Assign any records of 2.0 ha or under to be a spot ("y" under the spot attribute).

3. for records of 2.0 ha or less - if they have no tree number designation, then change them to "polygon" (therefore there may be some records of 2.0 ha or less that are designated as polygons).

4. for all records with a number of trees but without a percent attack, percent attack was calculated as following:

          calculated severity %  =   [#trees/(hectares*250)]*100
	  
          -where 250 equates to 250 stems per hectare, a commonly accepted figure representing average mature stocking in lodgepoly pine stands - commonly used for volume and/or tree # calculations with overview survey data.

5. All records were assigned a severity rating (L=light, up to 10% attack; M=moderate, 11-29% attack; S=severe, 30-100% attack) based on either the original percent attack figure, or the calculated percent attack figure (depending on which of these attributes it had a value for).

6. End up with a file where every record is designated as either a spot infestation or a polygon infestation, and where every record has a % attack and a resulting severity rating. Only records which origially had tree numbers will have a value for this attribute.