5. Georeferencing Forest Inventory into the FRA Geographic Information System

Not all of the inventories had a map with which it was possible to geographically locate the area inventoried. The reasons for this were different. The map was annexed in a separate document but this document was not found. The map should have been annexed with the report but the envelope-page was empty. The map was just a scratch map without coordinates. There was map of the global area inventoried but not of the different units or strata. Or only the coordinates of the fours corners were available.

In order to georeference the volume, depending on the information available, different procedures were applied.

In the case of a missing map, the description of the area was very useful and from this it was occasionally possible to understand and locate the area inventoried in a generic country map. Infact very often inventories’ limits were considered natural limits such as rivers, lakes, or administrative boundaries. Due to this, it was very important to invest time and energy to find country maps with the same information reported in the inventory description. In order to achieve this, the library (A.G.L.) was very useful. Normally the map used was at 1:500000/1000000 scale.

When it was possible to locate the area inventoried in a map with coordinates, the procedure was the following:

The borders of the area inventoried (the smallest unit for which the volume was reported) were drawn on an acetate with a 0.2 mm pen. In order to save time during the next steps, if the units were more than one block or additional inventories covered in a neighboring zone, they were included on the same lucid paper.

At least four tic marks (normally six or nine) were drawn on the acetate and their id and coordinates reported in a tixxxxxx.txt file (xxxxxx represents the id code).

The polygons drawn on the acetate were scanned at 200 dpi, and saved as a compressed .tif file (imxxxxxx.tif).

The files were imported into Arc\Info GIS and vectorized. For corresponding tic marks, tic points were added.

The cover was then edited to clean all the superfluous arcs. All the needed corrections were done.

To georeference the map, a cover of just tics was created and projected. Very few inventory maps included information on the projection system characteristics. When it was not possible to figure out the projection system, the projection characteristics of the topographical maps used in the respective countries was adopted. The cover with the polygons was "Transformed" on the tics cover earlier projected.

A new Item in the coxxxxxx.pat file was added to register the Id_gis code.

The polygon labels were added and coded with the Id_gis code.

When it was not possible to locate the area inventoried on a map, but the coordinates of the four corners were provided, the procedure consisted in building a cover of polygons directly from a .txt file where the coordinates of the fours corners were reported. The ID of the polygon reported in the .txt file corresponds to the Id_gis. In this way it was possible to avoid the labelling phase.

When two or more inventories covered the same area or part of it, to keep the polygons separate, and consequently the volume, the Region function of Arc\Info was used.