Sources of Geographic Information

Understanding GIS Data

Spatially referenced information has many important uses. Understanding where and what things are is necessary for efficient and effective planning and administration. Many maps and spatially referenced databases that are available to researchers are compiled for some governmental administrative purpose. Discovering these resources can be as easy as doing a web search in a web catalogger, such as Google Most cities of any size will have an official web site. Many now have GIS pages. 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

Lets say you find some GIS data. It is a bunch of files, how do you look at it? This is where you need to start learning about how to use GIS. At the Graduate School of Design, our primary GIS tool is ArcGIS. You can find all of the documentation including some introductory tutorials about GIS in the GSD's GIS Manual Documentation Page. The key to understanding GIS data once you have opened it in a GIS, is to zoom in on details, and to examine the Attributes for the features or cells.

Importance of GIS Metadata

Probably the first thing that you will notice is that the names of the items in the attributes table are likely to be cryptic and impossible to understand. The units and the referencing systems used to assign attributes to features are not clear, The precision of the geometry is not perfect (of course) but without understanding how or for what purpose (or when) the data were collected, you really don't know how to use these data! All of these questions should be answered by documentation that should be provided with the data. This Data about the Data is called GIS Metadata Whenever you get GIS Data you should be sure to get the metadata! Sometimes (but rarely) Metadata is actually part of the dataset (and may be browsed in ArcCatalog.) More often, the metadata is a web page or some other document that you should take care to save with your data.

General-Purpose GIS Data Resources on the GSD LAN

Every project needs to begin with a study of thre overall context. Data such as general shorelines and transportation. The easiest way to begin your gis database is with the collection of data that shops with ArcMap software. For a detailed description of building a contextual database for anywhere, consult the GSD On-Line Manual Page Beginning your GIS Database

ESRI Maps and Data

ArcGIS ships with 6 CDs containing hundreds of layers. These are handy for making maps, but also for general reference. The ESRI Data CDs can be found on the GSD network in L:\public\geo\esridata_9 Click here for a listing of the layers available on these CDs

Census Information for the US

Having set up your contextual framework, it will be very helpful to look at your area of interest in terms of demographics and housing. The GSD has the full line of CensusCD products accessible on the network. These make it easy to download census data from 1970 throu 2000, and to map any of thousands of geographical attributes as layers with your other gis data. For instructions on getting your census data, consult the manual page, Using Geolytics Products at the GSD. Though the Geolyics collection of tools provides the most comprehensive access to historic and current products of the deccinnial census, learning how to choose the variables you need from the tens of thousands avaialble can take a while to learn. If all you need is basic population and housing information, your easiest source would be The ESRI Maps and Data CDs

It is highly reccommended that you read the page Understanding and Mapping Census Data at the GSD before fooling around with census data!

Locations of all Businesses in the US, Downloadable by Zip Code and Business Type

The GSD has 5 licenses for a spiffy CD business directory that permits you to select from all the businesses in the 2000 yellow pages, and map them in ArcMap. For exhaustive instructions for using this resource at your PC or a public computer, see the on line manual page entitled, Using the Business Directory.

The Harvard Geospatial Library

We can be proud that our own Harvard Library Digital Initiative has a collection of thousands of geographic datasets and images that can be seartched and downloaded at The Harvard Geospatial Library (HGL). The curators of have recently made available a new tool for exploring their data collections directly through ArcGIS. You can learn more about this from The Harvard Center for Geographic Analysis web site.

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 exhorbitant 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:

The US Federal Government has very good information of a level of detail consistent with the 1:25,000 scale USGS Quadrangle maps. YOu can find loads of useful information, including low cost aerial photography of practiaclly any US city, at USGS Seamless Data Viewer. is a new and growing source of information regarding terrain and land cover information, nationwide, and aerial photography for selected areas. and USGS Earth Explorer. For digital terrain information for anyplace in the US. check out the GSD On-line Manual page, Obtaining and Assimilating Digital Elevation Models.

A good Source of data for europe and africa is found at The United Nations Environnment Progarm GIS Data Bank.

Georeferenced Images

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.

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 avaialble on the web. Find the GIS section of the state, city, or county's official web site.

Detailed Data of Local Interest

For local data, it helps to have connections. Studio instructors should cultivate their local connections well in advance of the start of their studio to try to obtain detialed local data. Each term we try to collect data that has been gathered. This collection is stored on the shared network volume l:\public\geo. You can find descriptions of the datasets stored there in the Geo Catalog. If we don't happen to have the data you need, in our collection, or if it is not covered by one of the general sources listed above, then you will have to make some friends in the local GIS establishment in your area of interest. Please make sure to ask for metadata for the information you get, and please make sure that the data get archived in the GSD's data collection when you are finished!

Miscelaneous

NeighborhoodScout is a commercial site that compiles together information from many sources to provide profiles for neighborhoods across the county. Before going there, click here to get your special GSD password (sorry, users's off the gsd net will not be able to see this page. Then go here: NeighborhoodScout is a commercial site that compiles together information from many sources to provide profiles for neighborhoods across the county.