View source for Exercise: Estimating forest area of county Göttingen based on digital landscape model (DLM) and administrative boundaries 1: 250 000

Since 2013 the federal government of Germany has published the ordinance to determine the conditions for use and provision of spatial data. A couple of spatial data products are provided free of charge for download or online use by [http://www.geodatenzentrum.de/geodaten/gdz_rahmen.gdz_div?gdz_spr=deu&gdz_akt_zeile=5&gdz_anz_zeile=0&gdz_unt_zeile=0&gdz_user_id=0 Bundesamt für Kartographie und Geodäsie in Frankfurt (BKG)]

== Use of digital topographic map 1:250 000 as web map service (WMS) ==
Digital topographische maps describe topographical objects of the landscape and relief of the earth's surface in raster format.
# Add a WMS dataset. Click [[file:QGIS_2.0_WMS.png|25px]] {{button|text=Add WMS Layer}} or {{mitem|text=Layer --> Add Layer --> Add WMS/WMTS Layer}}. Fill in the connection details. Name: {{typed|text=WMS dtk250}}, URL: {{typed|text=<nowiki>http://sg.geodatenzentrum.de/wms_dtk250</nowiki>}}. Click {{button|text=Connect}}. Select Layer ID: {{typed|text= 01}}, Name: {{typed|text=dtk250}}. The topographic map 1:250 000 of Germany is loaded (Fig. A). Zoom out to a larger overview.[[Image:dtk_250_goe.png|250px|thumb|right| '''Figure A:''' Digital topographic map 1:250 000. Source: http://www.bkg.bund.de
©GeoBasis-DE / BKG 2016]]

== Use of digital landscape model and administrative boundaries 1:250 000 as web feature service (WFS) ==
# Click [[file:QGIS_2.0_WFS.png|25px]] {{button|text=Add WFS Layer}} and Server connections {{button|text=New}}.  Fill connection details. Name: {{typed|text=WFS dlm250}}, URL: {{typed|text=<nowiki>http://sg.geodatenzentrum.de/wms_dlm250</nowiki>}}. Click {{button|text=Connect}}. Mark the row with TITLE = {{typed|text=OBJART_43002_f01}} (Forest). Click {{button|text=Add}}. Be patient: all forest area objects of Germany are now downloaded as vector polygons. When the download is finished, click {{button|text=Close}}: the polygons are displayed in the viewer. Full explanation of the object codes and classification scheme can be found in [http://sg.geodatenzentrum.de/web_download/dlm/dlm250-aaa/dlm250-aaa.pdf german] or  [http://www.geodatenzentrum.de/docpdf/dlm250_eng.pdf english] docs. 
Examples for modelling classes of feature type Nr. 43002 (forest) are given: 
#* [http://www.geodatenzentrum.de/geodaten/modell_adv.disp_pdf?gdz_sort_id=575 Waldverjüngungs-, Neuanpflanzungsfläche]
#* [http://www.geodatenzentrum.de/geodaten/modell_adv.disp_pdf?gdz_sort_id=572 Waldbestattungsfläche]
#* [http://www.geodatenzentrum.de/geodaten/modell_adv.disp_pdf?gdz_sort_id=113 Laubholz]
#* [http://www.geodatenzentrum.de/geodaten/modell_adv.disp_pdf?gdz_sort_id=114 Nadelholz]
#* [http://www.geodatenzentrum.de/geodaten/modell_adv.disp_pdf?gdz_sort_id=115 Laubholz und Nadelholz]
# Click [[file:QGIS_2.0_WFS.png|25px]] {{button|text=Add WFS Layer}} and Server connections {{button|text=New}}. Fill in connection details. Name: {{typed|text=WFS vg250}}, URL: {{typed|text=<nowiki>http://sg.geodatenzentrum.de/wfs_vg250</nowiki>}}. Click {{button|text=Connect}}. Mark the row with TITLE = {{typed|text=Kreis}}. {{button|text=Add}}. All county boundaries of Germany are downloaded as vector polygons. Click {{button|text=Close}} and the polygons are displayed in the viewer. Open the attribute table of layer {{typed|text=Kreis}} by marking the layer name and right click. In the attribute table menu click [[file:QGIS_2.0_Select_features_expression.png|25px]] {{button|text=Select features using expression}}. Type the expression {{typed|text="GEN" = 'Göttingen'}}. Click [[file:QGIS_2.0_Move_selected_top.png|25px]] {{button|text=Move selection to top}}. The county Göttingen is now selected. Mark layer '''Kreis''' in the layer panel. {{button|text=Save as ..}}. Type path and a new file name {{typed|text=Landkreis Göttingen}} and check the box ''Save only selected features''. {{button|text=OK}}.

== Calculating forest area of county Göttingen ==
# Clip forest area of Germany with county area of Göttingen. {{mitem|text=Vector --> Geoprocessing Tools --> Clip}}. Input vector layer = {{typed|text=OBJART_43002_f}}, Clip layer = {{typed|text=Landkreis Göttingen}}. Output shapefile = {{typed|text=OBJART_43002_f_clip}}. {{button|text=OK}}. (Fig. B). [[Image:Landkreis_Goe.png|250px|thumb|right| '''Figure B:''' Forest area (green diagonal hatch) and county area Göttingen (red) 1:250000 overlaid on Google Satellite layer. Source: http://www.bkg.bund.de ©GeoBasis-DE / BKG 2016]]
# Calculate area and perimeter for the clipped forest polygons. {{mitem|text=Vector --> Geometry Tools -->  Export/Add Geometry Columns}}.
# Calculate the sum of the column ''AREA'' in the ''OBJART_43002_f_clip'' layer.  {{mitem|text=Vector --> Analysis Tools -->  Basic Statistics}}. Divide the result by the total county area given in column ''Shape_area'' of the attribute table of layer ''Landkreis Göttingen''. What is the percentage of forest area in county Göttingen?   
[[category:Forestry Application]]