Massachusetts Institute of Technology - Department of Urban Studies and Planning
11.188: Urban Planning and Social Science Laboratory
11.520: A Workshop on Geographic Information Systems

Network Analysis, Advanced Raster, and Projects

April 11, 2018

 

Administrative

  • Lab #7 (GPS field work): due Monday, April 23
  • Homework #3: Raster Analysis and ModelBuilder
    • Part 1 (raster) due Wed., April 18
    • Part 2 (discussion and model builder) due Wed.. April 25
  • Project proposals: get feedback from us today, Friday (3-5 in 9-255), or via Stellar prior to next Wednesday (April 18)

Outline for Today

  • Lab #7 notes
  • Converting X/Y lat/lon data into point shapefiles
  • Network Analysis
  • Introduction to Web Mapping with Leaflet by Eric Huntley

Lab 7 Announcements

  • Lab #7 due Monday, April 23:
    • CSV files from field work are available on Stellar in 'materials' section
      • Separate files for each neighborhood plus one combined file
    • Upload into Excel and manipulate (per lab #7 instructions) before adding to ArcMap
    • Today, we will demo creation of point shapefile from lat/lon columns
  • Your submission should include three complete maps (make sure to include all map elements), featuring your observations on “land use”, “community characteristics”, and “physical conditions”, on separate maps. In addition, include one paragraph summarizing your findings. This should describe the information that you have noted in each of the three maps. Each of these maps should include the original track points, the line trajectory, the polygon(s) that summarize your analysis, and a few photos taken with  Mobile Forms to describe the type of observations made. The layout of these documents should be prepared in ArcMap, with no need to use additional graphic design software. You should submit ONE PDF per group, including your three maps and the names/roles of all members of the group.
  • See detail instructions for Lab 8 here.

Shapefile from X/Y points
  • Illustrate conversion of lat/lon values in table into shapefile of corresponding points
  • Issues:
    • Need to pull latitude and longitude out of 'location' field
    • Use Excel functions (explained in exercise): =MID(G2, 5, 9)  and =MID(G2, 21, 10)
      • But, they get extracted as text.  Convert to numeric (e.g., =1.0*b2...)
    • Add adjusted worksheet from Excel into ArcMap
      • Right-click: Display XY data to convert to points
      • Remember to specify geographic coordinates (lat/lon, North America, NAD83)
      • Results is an 'events' layer
    • Still need to "Data / export data' into a shapefile before it is saved as a real shapefile

Network Analysis

Some additional information regarding Network Analysis from previous lectures that can be useful as further reference for Lab 8.

  • Encoding proximity using a network (or graph) model, facilitates certain types of connectivity analyses
    • Find shortest path along streets from Point A to Point B
    • Find shortest path through N cities (Traveling Salesman problem)
    • How far can you get in 30 minutes
  • Many transportation analyses use network data models
  • Many hydrological analyses use network data models (runoff, flow, ...)
  • Additional information on Network Analyst below


Network Example: using US Census Bureau, TIGER Line Files

  • Geocoding Strategy using TIGER
    • Encode road network as street centerlines links connecting nodes (usually intersections)
    • Attach address information to each street segment
    • Use 'in reverse' to match street address to street segment to get approximate X,Y location
  • TIGER: Topologically Integrated Geographic Encoding and Referencing system
    • Examine attribute table and note columns for to/from information
    • http://www.census.gov/geo/www/tiger/
    • US Census Bureau TIGER line file 2000, technical documentation
      • at Census: http://www.census.gov/geo/www/tiger/rd_2ktiger/tgrrd2k.pdf
      • in class locker: http://mit.edu/www/data/census2k/tiger_tgrrd2k.pdf
  • Illustrative Example
    Street centerline road segments
    Attaching address ranges to road segments

 

What is a Network?

A network is a system of linear features connected at nodes
E.g, nodes could be where three or more street segments intersect.
The linear feature connecting any given pair of nodes is called an arc, or network link.
Each arc on a network is represented as an ordered pair of nodes, in the form from node i to node j, denoted by (i, j), and thus has direction.
A network representation that is good for transportation modeling may differ from a geographically accurate representation of the physical road (e.g., street centerline, handling exit ramps, 3D overpasses, etc.)

 

Other basic elements of a network:

A shortest path is the shortest (or least 'cost' path) from a source node (origin) to a destination node.  In practice, pathfinding seeks the shortest or most efficient way to visit a sequence of locations.

A tour is an enclosed path, that is, the first node and the final node on the path are the same node on the network.

A stop is a location visited  in a path or a tour.

Events or locations may be viewed as collection points (e.g., 'origins' or 'destinations' ) where certain resources are supplied or consumed.

A turn on a network is the transition from one arc to another arc at a node (there are 16 ways in which two intersecting roads can allow vehicle flow among the 4 links that 'connect' to the one node).

'Location-allocation' models often use network representation of connected places in order to determine the optimal locations for a given number of facilities (e.g., stores, restaurants, banks, factories, warehouses, libraries, hospitals, post offices, and schools) based on some criteria, assign people to the the 'nearest' facility.

  • For Lab #7, you need to run the shortest path algorithm to connect your observation points (in sequence) for each smartphone that was reporting to Mobile Forms. 
  • Another common task is to create a 'service area' that comprises all places that can be reached within X minutes from a specific location.  For example, how far from 77 Mass Ave can I get on public transit within 30 minutes.  Take a look at the 'Make Service Area Layer' tool in the 'Analysis' section of Network Analyst.


Introduction to Web Mapping with Leaflet    

  • Eric Huntley will illustrate web mapping of your field work data with Leaflet
  • The dataset with HTML files and data are here:
    • duspviz.mit.edu/resources/leaflet_tutorial.zip
  • This (and many other) tutorials are available on
  • Here is today's tutorial (with coffee shops instead of your field work points)



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