Cultivating Spatial Intelligence
Sources of Spatial Data
Most projects begin with a search for base data. This lisiting will begin with a few sure-fire sources of data that you can use to build a contextual dataset for a city. We will then work up to strategies for finding more detailed data. One thing to always keep in mind: since you are going to invest time in pulling data together to study a place, you should organize your data well so that you and others can build on what you have done!
Discovering Geographic Data
The great thing about geographically referenced data is that datasets compiled by independent agencies can be combined together and will align with eachother in a coherent way. In addition to representing things graphically, GIS data includes attributes that reflect measurements, classifications or other observationsthat may be critical to understanding what things are and how they are related. Discovering these resources can be as easy as doing a web search. Many cities and government agencies now have sections of their web sites focused on Geographic Information Systems data. The likelihood of your finding free information about a particular area is usually proportional to the importance of that area to a government agency, and the willingness of that agency to make that information available.
Exploring GIS Data
When you finally find some GIS data, you will want to understand whether the data is suitible for your porposes or not. Critical aspects of a dataset should be addressed in the data documentation, or Metadata for example:
- The subject of the dataset?
- What time period is represented?
- Who collected the data and why?
You should always be sure to save the metadata for datasets that you download from the web! Without documentation the data that you download will be of little use later on. For a good tutorial on exploring GIS data and metadata, see Exploring Geographically Referenced Data
General-Purpose GIS Data Resources
Every project needs to begin with a study of the overall context. Data such as general shorelines and transportation.
OpenStreentMap The People's Map
The OpenStreetmap is a project that engages the public in the project of developing digital map data comparable with Google maps. The great thing about this project is that the data are freely available for applications outside of the web browser -- so, for ecample you can download GIS databases of teh openstreetmap data from GeoFabrik Web Site
GIS Data from Libraries
The Tufts Open Geo Portal is an exciting project that lets you search and discover thousands of datasets from several libraries.
Data from National and International Mapping Agencies
As our quest for data becomes more specific, the next most reliable source of data are national and international mapping agencies. Some of these public service agencies are very secretive or charge exorbitant prices for their data (for example, the British Ordinance Survey and its descendants around the world) which is a shame. But other agencies set a good example, For example:
Elevation Data The US Federal Government has very good information of a level of detail. You can find loads of useful information, including low cost aerial photography for the entire united states, at The National Map Viewer and Download Tool. is a new and growing source of information regarding terrain and land cover information, nationwide, and aerial photography for selected areas.
Bathymetry Data: For U.S. coastal bathymetry, check out The NOAA Estuarine Bathymetry download site.
A world-wide bathymetry dataset has been compiled by The General Bathymetric Chart of the Oceans (GEBCO) Their data is aviable for download from British Oceanographic Data Centre. Though this process is a bit convoluted and poorly documented. Users on the GSD network are encouraged to use our local copy of the GEBCO Bathymetry dataset with the GridView extraction sodtware located in goliath://geo/gebco_worldwide_bathymetry.
A technical tutorial on downloading and transfroming elevation data is covered in more detail on the web page, Digital Elevation Models.
More Global Sources
A good Source of data for Europe and Africa is found at The United Nations Environment Program GIS Data Bank.
A vast amount of information about places can be found in the form of digital images, either scanned maps or digital aerial photographs. Many sources of these are discussed on the The GIS Manual Page on Geographic Images Some of these images may have imbedded georeferencing information that allows it to be aligned with other data in the GIS. If not, then images may be georeferenced using techniques discussed on the Georeferencing Images.
Time Series Multispectral Satellite Images
The NASA Mission to Planet Earth project has produced nicely georeferenced series of relatively cloud free imagery covering the whole globe. The imagery, which can be downloaded from The University of Maryland Global Land Cover Faciltiy, is of fairly course resolution (30-60 meter cell size) but contains higher spectral resolution than most imagery, with a channel for infrared reflectance. These multi-chammel images can be tricky to work with, but if you are very patient, you can meld the various channels into useful graphical products and even do some classification of land cover and land use change.
State and Provincial Agencies
The more detailed the information you want, the less likely it is that you will find it for free on the web. At the state level, you may get lucky, and find a site like the Massachusetts GIS These days, even city governments are making their data available on the web. Find the GIS section of the state, city, or county's official web site.
Detailed Municipal Data
If you have clicked through some of the links provided above, you will have noticed that the world of geographical data is not well organized. At a world-wide scope, you may find generalized world-wide data. Ar a regional level, the data are more specific, but fragmented across administrative domains -- both in the buraeucratic and geographic sort. The same pattern of fragmentation is exacerbated at the local level. The Open Government and Open Data movements have helped to expose more geographic data of local interest on the web. For a few examples, see:
- City of Cambridge GIS Data
- City of Boston Open Data Site (Many datasets of geographical interest!
- City of Boston GIS Data
Compare and Contrast!For local data, it may be necessary to contact local officials to request data. Studio instructors should cultivate their local connections well in advance of the start of their studio to try to obtain detialed local data. Obtaining local data involves a number of steps. First, you should have a clear idea of the types of layers that are desired(e.g. building footprints, trees, edge of pavement, property parcels, contours, aerial photography, etc.) Then think about what local agencies might have these data. Of course, you would look on the web to see if data are available easily -- or to find contact information of the probable custodians of the data. Then one would write letters or make phone calls. When requesting data you should be very specific about what you would like to find. If you simply ask for GIS data you are likely to get a file of zip code boundaries for the area in question. Of course, you should also ask for metadata! Click Here for a boiler-plate data request letter that you can tailor to meet your purposes.