Using a GIS to Calculate Area of Occupancy. Part 2: Automated Calculation of the Area

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1 Using a GIS to Calculate Area of Occupancy Part 2: Automated Calculation of the Area By Erin Prescott British Columbia Conservation Data Centre, A NatureServe network program December 2008 This document describes the second step to be taken when using a GIS to calculate Area of Occupancy for NatureServe conservation status assessments. More specifically, the instructions below describe how to use GIS to automatically calculate the area value needed for the status factor assessment using a 2 km x 2 km grid, and were developed for NatureServe network programs that use the Biotics 4 Mapper application. This procedure has been developed to utilize grid cells created using the process described in the document Using a GIS to Calculate Area of Occupancy Part 1: Creating a Shapefile Grid by Ryan Elliott. Questions and further information related to the instructions that follow can be directed to Erin Prescott (erin.prescott@gov.bc.ca; Ecosystems Branch, Ministry of Environment, P.O. Box 9358, Station Provincial Government, Victoria, V8W 9M2, Canada). A basic knowledge of the ESRI ArcGIS software and associated tools (e.g., Spatial Analyst) is required to use these instructions. Note that these instructions, developed in 2008, utilize ESRI ArcInfo v.9.2 software. As applications are constantly evolving, the applicability of this documented process may change. Please check the NatureServe website or contact the author for the latest edition of instructions. Software Requirements: ESRI ArcInfo (instructions developed for version 9.2) Spatial Analyst Extension Steps: 1. Create a grid of your province, state or area of interest following the steps described in R. Elliott s document Creating a GIS Grid Shapefile. 2. Export Source Feature shapefiles from Biotics Mapper, so they can be used in ArcGIS. Source Features are used, as they are the initial features digitized in Biotics to represent element locations. a. In Mapper, Convert to Shapefile the following themes: EO.Source Lines, EO.Source Points, and EO.Source Polygons. b. The following fields should be included in the export: Scientific Name, Common Name, Element Subnational ID, EO Rank, and EO Type. In order to have the above fields included in the Source Feature layers you will need to join the following tables to the SF shapefile: EO_Source_Feature, EO, and 1

2 D_Basic_EO_Rank_ID. In Mapper; Biotics; Add/Remove Oracle Attributes (see specifications below). 3. In ArcGIS, buffer the Source Feature Lines and Source Feature Points by 1m, in order to allow the three source feature shapefiles to be combined. a. ArcToolbox; Analysis Tools; Proximity; Buffer. 2

3 4. Merge the three Source Feature shapefiles into one polygon shapefile. a. In ArcToolbox; Data Management Tools; General; Merge. 5. Exclude all Source Features/EOs that have been extirpated a. Select by Attribute ; EO Rank <> X; Data Export Dat.a 6. Join the grid shapefile and the source feature shapefile into one shapefile. a. In ArcToolbox; Analysis Tools; Overlay; Spatial Join to combine the shapefiles. The Target Features is the grid of your area of interest. The Join Features is the source feature layer (which excludes extirpated occurrences). You will want to Join-one-to-Many (as there can be many Source Features within one Grid). b. You can also use Union if you d like a spatial representation of the data. 3

4 7. Dissolve the shapefile so that each element is only represented once in each grid. a. Use ArcToolbox; Datamanagement; Generalization; Dissolve. Dissolve the shapefile on Grid ID and Scientific Name (or Element Subnational ID). 8. Calculate the area for each Grid_ID and element combination (each should equal four km square). a. Add a field to the dissolved Grid/Source Feature Shapefile. b. In the table view use Options; Calculate Geometry. 4

5 9. Sum the area for each element to determine the AOO for each element. a. In the table view: Summarize; Field to Summarize = Scientific Name (or Element Subnational Rank); Area = Sum 10. You will now have a new table with one row for each element, and an area of occupancy for each element (the sum of the grid areas where each element occurs). 5