Web Services and Mapping APIs

April 7, 2021, Joseph Ferreira

Administrative

Lab #5 due today
Next draft of Project Proposal - due Monday, April 12
Homework #3 is due next Wednesday (April 14)

Today

Introduction to Internet GIS and GeoSpatial Web Services
- What do we mean by 'web mapping' or 'internet GIS'?
- Distinguish between map publication, single purpose apps, and geoprocessing (interactive spatial analysis)
- Decompose into server and client components
Demonstrate use of web services
- MassGIS web mapping services (WMS)
- QGIS use of web mapping services

Online tutorials for Web Mapping and Geoprocessing Services

by Eric Huntley (DUSP GIS specialist, ehuntley@mit.edu)

Web mapping and leaflet exercise

Make a Web Map Using LeafletJS

DUSPViz tutorial: http://duspviz.mit.edu/web-map-workshop/leaflet-js/
Lecture notes: http://duspviz.mit.edu/tutorials/web-maps-101

Internet GIS and GeoSpatial Web Services

Introduction to Internet GIS and GeoSpatial Web Services
- What do we mean by 'web mapping' or 'internet GIS'?
  - Yahoo Maps, Google Earth, Mapquest, etc. - are these GIS applications?
  - What about map 'mashups' on top of Google Maps and Google Earth?
  - What about Android and iPhone maps and navigation tools?
- Distinguish between map publication, single purpose apps, and geoprocessing (interactive spatial analysis)
Decompose into server and client components
- Recognize pros and cons of client/server workload balancing
- Recognize utility of open standards for interoperable geospatial web services
  - In this case, the web mapping service (WMS) protocol from the Open Geospatial Consortium (https://www.ogc.org/)
- Enter these MassGIS URLs in a web browser

http://giswebservices.massgis.state.ma.us/geoserver/wms?dpi=120&request=GetMap&layers=GISDATA.EOTMAJROADS_ARC&srs=EPSG:4326&bbox=-71.1,42.35,-71.0,42.37&width=1000&height=300&format=image/png&service=wms&transparent=true

http://giswebservices.massgis.state.ma.us/geoserver/wms?dpi=120&request=GetMap&layers=GISDATA.MBTABUSROUTES_ARC&srs=EPSG:4326&bbox=-71.1,42.35,-71.0,42.37&width=1000&height=300&format=image/png&service=wms&transparent=true

Do you recognize the meaning of the parameters? Play with the values...
- http://giswebservices.massgis.state.ma.us/geoserver/wms?

dpi=120&
request=GetMap&
layers=GISDATA.EOTMAJROADS_ARC&
srs=EPSG:4326&
bbox=-71.1,42.35,-71.0,42.37&
width=1000&
height=300&
format=image/png&
service=wms&
transparent=true

Note that some services only produce maps at particular scales
- Otherwise, get xml-tagged error message
MassGIS web services homepage: https://wiki.state.ma.us/display/massgis/Overview+of+MassGIS+Web+Mapping+Services+and+Applications

Demonstrate use of MassGIS web services from within QGIS
- In QGIS, choose 'Layer / Add Layer / Add WMS/WMTS layer'
- Click the 'New' tab to open 'Create a New WMS/WMTS Connection'
- Click the 'Connect' tab to open the URL
- The MassGIS web server will generate an image properly sized and georeferenced for your QGIS map window showing the major roads with standard symbols in a PNG format that has a transparent background so it can overlay your map.

Integrating web services within web pages:

Map mashups

Check out these sights:
- Zillow: housing price estimator ('Your edge in real estate')
  - http://www.zillow.com/
  - Try: 100 Vassar St, Cambridge, MA, 02139
  - How are maps and tables stored, queried, assembled? what is the business model?
- Walk Score: rating addressess for local walkability:
  - http://www.walkscore.com/
  - boston 'hot spot' map: http://www.walkscore.com/MA/Boston
  - Results for 200 Putnam St, Cambridge
    - http://www.walkscore.com/score/200-putnam-st-cambridge-ma
  - How are maps and tables stored, queried, assembled? what is the business model?
    - Transit calculation uses google transit API (discussed below)

Google maps APIs (application programming interfaces)
- Family of APIs to 'mashup' points, lines, and polygons on top of Google Maps and Google Earth
- Start here: Google Developors 'products' webpage: https://developers.google.com/products/?csw=1
- Google Maps APIs: https://developers.google.com/maps/
  - A free service - but read the 'fine print'
  - 'Terms of service': http://code.google.com/apis/maps/terms.html
  - Business use restrictions
  - What are risks to public agency that builds services with Google API?
- Google transit: http://maps.google.com/help/maps/transit/index.html#utm_campaign=en&utm_medium=ha&utm_source=en-ha-na-us-bk-trs&utm_term=google%20API%20directions

Deeper integration of geoprocessing services within web pages:

Examples of front-end tools that can access geoprocessing services:

Using URLs together with WMS protocols to grab map images: MS-Word, Adobe Acrobat, QGIS, ArcGIS
Using javascript libraries with WMS protocols: Leaflet, MapBox, Carto

Example of back end support for large, dynamic databases

Postgres + PostGIS for SQL compliant, multi-user, relational database management with spatial extensions
Illustrate use of postgres from QGIS - by redoing example from census lecture

Thematic map of median personal earnings from 2000 census
Geography: us_ma_e25blkgrpsct_2000 block group boundaries
Census 2000 data:

MAGEO table of geographic identifiers and summary levels
MA0007 table including LOGRECNO and P85 personal earnings data

Examine tables on PostGIS server (on VM at Medai lab)

Note X/Y boundary geometry (of polygons) is included in 'geom' column
Spatial Reference System (SRS) information for EPSG codes is in a separate table
Relationship between SRS and census block group boundaries is stored in a view

Join boundaries, mageo, and ma0007 with SQL query in PostGIS for summary level 150

create table c2000inc as
(select g."LOGRECNO",
        e."P085001", e."P085002", e."P085003",
        g."STATE"||g."COUNTY"||g."TRACT"||g."BLKGRP" AS blkkey
   from census2k.mageo g,
        census2k.ma00007 e
  where g."LOGRECNO" = e."LOGRECNO"
    and g."SUMLEV" = '150');

Pull result into QGIS, join to boundary layer and thematically map

These tools are useful for 'publishing' project work

Enable interactive manipulation of maps within browser, PDF document, etc. without 'running' GIS software

See DUSPviz tutorial:
Web Mapping workshop tutorials: http://duspviz.mit.edu/tutorials/
Leaflet tutorial: http://duspviz.mit.edu/web-map-workshop/leaflet-js/
Carto: additional libraries plus backend PostgreSQL (PostGIS) database access
See DUSPviz Carto tutorial: http://duspviz.mit.edu/web-map-workshop/databases-leaflet-cartodb/
ESRI ArcOnline web services (available from MIT via Rotch Library)

Created by Joseph Ferreira and Michael Flaxman, 2006-2007
Last modified 19 March 20158 Joe Ferreira
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