Introduction to Quantum GIS

Transcription

1 An Overview: Workbook 2 Dr. Arthur J Lembo Jr., Eric Flint, John O'Brien, Alex Nohe 3/19/2013 Quantum GIS is a fully functional and modern Open Source desktop GIS package. This introduction to Quantum GIS will illustrate some of its basic capabilities through application of a practical tutorial.

2 Setup: To complete the following workbook, Quantum GIS must be installed on your computer. It can be downloaded at: Additionally you must download a local copy of the data files from github at: Task Three: Demographics Analysis Proponents of the concept of environmental justice have found evidence to suggest that certain minority groups bear a disproportionate burden of environmental toxins. We ll explore this in Richland County, SC. Select those census blocks that contain a TRI facility and calculate the total number of people living in the selected census blocks with a TRI facility. Based on the total number of people living in census blocks containing a TRI facility, calculate the percentage of people who are white and who are nonwhite. You will have to use the databk79.dbf file to find your answer. 1) Select by location (Census Blocks containing TRI facilities) Vector Spatial Query Spatial Query 2

3 Select source features from = bk79 Where the feature = Contains Reference features of = tri92 And use the results to = Create new Selection Apply * This GUI will appear Apply Close * bk79 selected will render to map and appear in layers 3

4 * Remember that this New Feature Class is created in Virtual Memory Only! Tables cannot be edited, must be saved as a shapefile if editing capabilities are needed. We will convert this feature classes to a shapefile after we perform the join* * By R on the new layer and Rename you can label the new layer bk79_tri92 Virtual to avoid confusion with other layers 2) Join * In order to complete the demographics analysis required by this task you must first join bk79_tri92 s Virtual table to databk79.dbf R bk79_tri92 Virtual Properties Joins Tab 4

5 * This GUI will appear Join Layer = databk79 Join Field = TRBK Target Field = TRBK [X] Cache join layer in virtual memory OK * Join will be added to Layers Properties GUI 5

6 OK * databk79 s fields will be joined to bk79_tri92 Virtual attribute table 3) Save bk79_tri92 Virtual as a shapefile for analysis R bk79_tri92 Virtual Save As 6

7 * This GUI will appear 7

8 Format = ESRI Shapefile Save As Browse Select appropriate path and name for shapefile (bk79_tri92) X Add saved file to map OK *Map will render with new shapefile in layers 8

9 * Attribute table will include databk79 fields and be editable (editor button on toolbar will not be grayed out) 4) Edit Attribute table and Calculate/Analyze Demographics (Add Column / Field Calculator) R bk79_tri92 Open attribute table * Attribute Table will open 9

10 Edit button on table toolbar Field Calculator X Create New Field Output Field Name = PercWhite Output Field Type = Decimal Number (real) Output Field width = 10 Output Field Precision = 2 ( Functions List Fields and Values white_ / Functions List 10

11 Fields and Values population ) * in Expression Field and type in 100 after * sign * Expression = ( white_ / population ) * 100 OK Save Edits Field Calculator X Create New Field Output Field Name = PercNW Output Field Type = Decimal Number (real) Output Field width = 10 11

12 Output Field Precision = 2 ( Functions List Fields and Values white_ / Functions List Fields and Values population ) * in Expression Field and type in 100 after * sign * Expression = ( nonwhite_ / population ) * 100 OK Save Edits Editing Mode Button to exit editor Close 12