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Using rare element occurrence (EO) quarter quad location data with QGIS

Using rare element occurrence (EO) quarter quad location data with QGIS

In this tutorial you will first make a shapefile of EOs by quarter quad. Then there are sections on quarrying and using the new shapefile as well as making a range map of Bald Eagles in Georgia. While using this tutorial you will need to download qq.zip and qq_eos.csv from our website. Unzip qq.zip into its 4 component files (qq.shp, qq.shx, qq.dbf and qq.prj) that make up the quarter quad index shapefile.

Remember, when you are finished entering data in the following dialogs, click OK as you exit out.

Make a shapefile of EO records with quarter quad rectangles as each record's associated shape using QGIS 1.7

Installation and setup

  1. Download and install QGIS 1.7.x if it is not already installed.
  2. Install the QGIS Table Manager plugin if it is not already installed. To install go to Plugins/Python Plugins on the menu. The Table Manager plugin is in the QGIS Contributed Repository. If you need help installing and using plugins please see this tutorial.
  3. Make sure the extensions toolbar is turned on under View/Toolbars on menu.

Rename fields in qq.shp

You need to rename the fields in qq.shp to prevent field name clashes when exporting the data to a shapefile later on.

  1. Download and place
  2. Bring qq.shp and qq_eos.csv into Quantum GIS using the Add Vector Layer button.
  3. Click on qq in the TOC (Table of Contents) to make it active and click on the Table Manager icon on the Plugins Toolbar.
  4. In the Tables Manager dialog rename the fields in qq.shp as follows:
    • area_code to qq_code
    • area_name to qq_name
    • rpt_name to qq_rpt_nam

Export a copy of qq.shp to CSV  geographic format

Comma separated value, CSV , format is a type of delimited text format where fields are separated by commas and records are separated by line returns. Generally, if a field value contains commas, double quotes or certain other special characters then the value is surrounded by double quotes. Then if the value contains double quotes, each double quote is converted to a pair of consecutive double quotes". This delimited text format is sometimes called Microsoft Excel csv format. 

  1. Right click on qq in the projects TOC and select Save As...
  2. In Save Vector Layer As dialog enter the following for the fields:
    • Format: Comma Separated Value
    • Save As: path and the file name, qq2.csv
    • Layer: GEOMETRY=AS_WKT
    • (use default values for other fields)
  3. Open the file you just created using Add Vector Layer button.

You may notice that when you open qq2.csv into QGIS, even though it is only a text file, it opens as a Geographic layer with quads showing on the map. This is because QGIS sees a field named WKT and uses this value to represent the geometry of each record on the map.

Join qq_eos.csv data with qq.csv data

  1. Double click qq_eos in the TOC to open the Properties dialog and select the Joins tab.
  2. Click the green plus button near the upper left to create a new join
  3. Enter the following in the Add Vector Join dialog
    • Join Layer: qq2
    • Join Field: qq_code
    • Target field: id_code
    • (use default values for other fields)

Export qq_eos making it a geographic CSV file.

The geometry field named WKT (for Well-know Text) containing well-know text of the associated quarter quad geometry makes this a geographic layer file that QGIS will open and use the value in the column named WKT as the vector geometry to represent each record on the map. See the article for well-know text in Wikipedia for more information about the well-know text, OGC standard. You can view the well-known text for each quarter quad by opening the attribute table and looking at the value in the WKT field.

  1. Right click on qq_eos in TOC and select Save As
  2. Format: Comma Separated Values
  3. Save As: a path plus qq_eos_geo.csv as the file name
  4. (use default values for other fields)

Open the new Geographic CSV file, qq_eos_geo.csv, using Add Vector Layor button. You will now see that all EO records have their associated quarter quads displayed on the map

To make an EO quarter quad ESRI shapefile

  1. Right click on qq_eos_geo in TOC and select Save As...
  2. Format: ESRI Shapefile
  3. Save As: path and file name
  4. CRS: Click Browse and under Search enter 26917 and press Find. This is the ID code for NAD83 / UTM Zone 17N, the coordinate reference system of the data. Alternately, you can navigate through the coordinate reference systems in this window to select the projection.
  5. (use default field values for other fields)

This qq_eos shapefile can now be used in QGIS or many other GIS and mapping programs and viewers to do analysis of the locations and range of rare species and natural communities in Georgia.

Using selected EO records in QGIS in a spreadsheet program.

  1. Select one or more quarter quads on the map. (Using "Select Single Feature" will only select one record at the location you click. Use another selection method like "Select Features by Rectangle" to select all records within a single quarter quad).
  2. Open the attribute table and press Ctrl-C (hold down the Ctrl button and tap the letter c on the keyboard) to put selected records into the clipboard.
  3. Data in clipboard now has EO records with fields delimited using Tab characters.
  4. Paste it into a spreadsheet such as Microsoft Excel or Libra Office Calc for further sorting, filtering, analysis and printing.

Make a shapefile of EO records with quarter quad rectangles as each record's associated shape using QGIS 1.7

  1. Right click on qq_eos_geo in TOC and select Query...
  2. Using the query builder, double click on SCOMNAME
  3. Press the equals button which will insert an equals sign in the SQL Where Clause field after SCOMNAME
  4. Type Bald Eagle within single quotes at end of the Where Clause
  5. The SQL Where Clause field should now read: "SCOMNAME" = 'Bald Eagle'
  6. Click the test button and if everything looks good, press OK.
  7. You now have a nice map showing Bald Eagle locations in Georgia using the quarter quad data.

If your are interested in improving your skills with QGIS, there are many text and video tutorials about QGIS on the web; use your search engine to find them. The QGIS manual is very good too.

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