Recent events at MIT

The recent deaths of two undergrads are particularly upsetting. Please come talk with me if these events impacted your progress with this class, or if you would just like to talk with someone besides your classmates about life and work at MIT.

Key Ideas in Lab #4:

1. Mapping population density with too-detailed a map -- handling one-to-many relationships in ArcMap
   • Tricky to map population density when towns may have more than one part (polygon).
   • Common complication since geometry and data tables come from different sources
   • More common with detailed (large scale & small area) maps - Boston has more than one 'part'
2. Constructing meaningful indices (such as population density)
   • Requires excluding cases and normalizing data
   • May require creation of new features and attributes in writeable directories.
3. Charts and business graphics in ArcMap
   • Another useful dimension: business graphics
   • Careful about which data gets mapped
     • Understand the one-to-many linkages among tables
     • Be aware of selected sets in maps and tables - most operations act on selected sets and you may forget about the selections
4. Handling one-to-many relationships in MS-Access
   • Equivalent to 'summarize' command for ArcMap attribute tables (but more powerful)
   • Need to turn on 'totals' row in the query builder GUI
   • 'Group by' the column(s) you want to collapse into one unique value per row
   • Specify an aggregation function for the other columns (count, sum, average, minimum, ...)

Key Techniques in Lab #4:

1. Joining attribute tables in ArcMap
• Identify matching columns for each table
• Direction matters! start with geographic table
• Join operation will ignore >1 match to any mapable row!
2. Summarizing ArcMap attribute tables:
• Aggregate/summarize all the other attributes for the rows that have the same value in the 'summarize' column
• Highlight the 'group by' column (where each unique value results in one output row)
• Select other columns that you wish to aggregate (via 'count,' 'sum,' 'max,' etc.)
3. Charting the correct table
   • May need to 'summarize' a table before charting
   • Be careful about which table to join to maps (i.e., the one-to-one table after summarization)
   • Selecting on map can impact chart as well as highlighting attribute table rows (if correct tab is checked)
4. Moving tables from ArcGIS into MS-Access

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