• Examine the location patterns of Cambridge stores by using the 'spatial join' tools to tag store location data (bookstores, ice cream shops, record stores) with the demographic characteristics of their neighborhood. (This is a 'point-in-polygon' operation.)
• Estimate the number of children living near Ames Street by:
  • Creating a buffer around Ames St.
  • Intersecting the Ames street buffer with the Cambridge blockgroup data
  • Apportioning children in each block group that is split by the buffer in proportion to the block group area in the buffer

Before we start:

• Download 11.188_lab4_data.zip from Stellar; extract into your working directory, and open 11.188_lab4_start.qgz...
• Rounaq will provide comments on Lab #2
• We will discuss the maps listed on today's 'startup' page:
• Who should set what 'rules' regarding the maps that appear online?
• Smelly places in Boston (from Nicole): https://twitter.com/ArchivesBoston/status/1367914121371422720
• Noisy kids in Japan (from NYTimes): https://www.nytimes.com/2021/02/25/world/asia/japan-noise-map.html?searchResultPosition=1
  
• Tension over corporate influence on OSM (from Bloomberg):  https://www.bloomberg.com/news/articles/2021-02-19/openstreetmap-charts-a-controversial-new-direction?cmpid=BBD022521_MAPLAB&utm_medium=email&utm_source=newsletter&utm_term=210225&utm_campaign=maplab

Lab #4 Issues:

• 11.188_lab4_start.qgz project document has two new features:
• Orthophotos (from WMTS-compatible web server at MassGIS)
• QML-formated file that save style information for QGIS: camb_lu21_style-massgis2.qml
• Use 'style' button at bottom of layer properties 'symbology' tab to save/load styles
• Join-by-location is different from select-by-location. Joining actually moves attribute information across layers. Selecting only affects which features are displayed (and which features can subsequently be exported or operated upon).
• Buffering Ames St. is similar to previous buffering done on Mass Ave
• Apportioning Cambridge children to the parts of each block group that falls within the buffer.
  • Union and Intersect operations retain the old polygon areas.
  • You need to compute the new-polygon areas after the buffer cuts the block groups into smaller sections.
  • The Field Calculator tool and geometry options simplify the area calculations.

General QGIS Tips:

• Folder, shapefile, and table names:
  • Use only letters and numbers with NO spaces, special characters, etc.
  • Start all names with a letter.
• Save early and often:
  • Always have a recent unused copy of any QGZ documents (the project document that saves everything except the datasets).
  • Every time you start an QGIS session from a saved document, save it right away into an new document with a new name (version2, ver3, or with the session's date).

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Last modified 2017- 2021 Joe Ferreira and Juan Camilo Osorio.