Looking at the Inventory

We can take a look at the fragments file using the Map Viewer included in Patchworks.

  1. Select "Map Viewer" from the Application Launcher within the Output folder and click on "Go". Alternatively, you can also drag and drop your fragments.shp file into the map viewer window.

  2. Click on the Add a layer button and then with the "Shapefiles" tab active, select QuickTourIII/data/fragments.shp

The polygon lines of this layer will display when viewed at a scale of 10,000 or larger. Scale thresholding is set in the map symbology and is used to avoid clutter when viewing maps at smaller scales.

  1. Using the Zoom in button from the toolbar, click and drag a small box near the upper left portion of the landbase. The size of the box you draw determines the scale of the map, make sure the scale is less than 10,000. At this scale, you will see the black polygon lines of the inventory

  2. Select the layer in the Legend panel so that the border appears raised. This will activate the Layer specific tools in the main toolbar.

Figure 148. Map Viewer, showing inventory layer

The inventory polygons will display when zooming in to a scale larger than 10,000.

  1. Now click on the Show Table button on the Map Viewer toolbar to open the Table Viewer for the inventory.

    If the 'Show Table' icon is not visible it is because the layer is not selected in the Legend panel of the Map Viewer. Click on the 'Fragments' layer so that it appears to have a raised border. This will activate the 'Show Table' icon in the toolbar.

You will be viewing an attribute table of the fragments file. This file has 119,735 polygons, many of which have the same age and forest unit. Most fields will not be used by the model. We will want to group similar polygons to make candidate blocks a more reasonable size for allocation; small stands that are only a fraction of a hectare would be unrealistic to harvest on their own, for example. We will want to make the model smaller by lumping adjacent similar polygons. On the other hand, if the dataset contains polygons that are much larger than the size of a harvest block, sometimes polygons must be split.

  1. Use the scroll button on the bottom of the screen to scroll back and forth to view all the fields in this layer. Click on the area field and sort the dataset by clicking on the sort records in ascending order button to view all the smallest polygons on top.

The field in this dataset represents polygon area in m2. The smallest polygon is just over 1000m2 (0.1 ha) in size. If there were many polygons of this size or smaller present in the dataset, you could consider eliminating them (merging them with neighbouring polygons) in a GIS procedure to "clean up" the dataset and reduce the number of polygons before blocking.

  1. Click on the AREA field if it is not active and sort the dataset by clicking on the heading "sort records in descending order" button to view all the largest polygons on top.

There are 21 polygons larger than 100 ha in size. Examining the columns to the far right of the table, we can see that all these polygons are not forested (Theme5 = NS) so we do not need to split any polygons in this dataset. For more information on splitting polygons, see Polygon Splitter.

We will need to use only 10 of these fields in order to block the fragments into Patchworks blocks; the first step in building a Patchworks model. Since this inventory was also used for the aspatial model Woodstock, several of the fields we are interested in have a "Theme" tag.

  1. Find and familiarize yourself with the following fields in the table to prepare for grouping fragments.

Table 3. Fields required by the group fragments tool

Required field to group fragmentsField name in inventory
Unique fragment identifierFRAGS_ID
Fragment eligibility criteriaTHEME2 (Query: THEME2 ne 'N')
Area columnAREA
Age columnF_AGE

We are almost ready to use the Group Fragments tool to group polygons. But before doing so, we will have to create some topology for the fragments!