This is the second in a series of columns on real estate information sources. The topic this time is digital data. I will define the topic, delineate the many types of digital data, and conclude with data sources.

As used here, digital data refers to maps-e.g., zip code zones, census tracts, streets, individual buildings-displayed on a computer monitor or printer. Everything on each map is defined by one or more longitude-latitude coordinates, state plane coordinates, or cartographic coordinate system. Without becoming too technical, such maps are vector files, in contrast to aerial photographs, satellite images, and other raster files (which will be discussed in a future column).

Innumerable types of digital data exist. Anything that can appear on a map can be digitized. In real estate, the most frequently used digital files are these:

• Zip code zones, census tracts and census block groups-for thematic maps of socioeconomic variables that correlate to the demand for real estate, including population growth, household income, unemployment rates, and so on;
   
• Street networks-for reference purposes (to help viewers identify the area that the map covers), address matching (software that automatically identifies the location of a property based on its street address), and analysis of traffic volumes; and
   
• Individual properties-sometimes covering a large area, such as a subdivision, and other times a single coordinate point, representing a single residential or commercial building.

Other files that are employed less frequently (because they are not conveniently available, are too expensive, and/or are not easily interpreted by users) include the following:

• State, metropolitan statistical area (MSA), county and city boundaries-for regional market research, market ranking, and trade area analysis;
   
• Submarket boundaries-again for market research et al., but at a more focused geographic level;
   
• Assessor parcels, general plan, zoning, land use, water and sewer network, capital improvements program, tax increment financing districts, etc.-to identify regulatory and infrastructural factors governing a property's development and resale;
   
• Flood zones, earthquake fault lines, toxic waste sites, rare and endangered species, archaeology sites, soils, and so forth-to identify any environmental constraints that could affect the use and value of a property; and
   
• Elevation contours-for reference purposes, and for conversion in more sophisticated GIS packages to three-dimensional renderings of a site, slope and aspect maps, cut-fill calculations, view shed analyses, etc.

Digital files that are only now beginning to become available but which will be extensively used by real estate professionals are the locational coordinates of individual properties plus comprehensive attribute information on square footage, acreage, number of stories, year built, type and quality of construction, ownership, assessed valuation of land and improvements, asking price (if any), selling price in previous transactions, and similar information published by select government agencies and other real estate data vendors.

Sources of data can be as diverse as the types of data. Broadly speaking, real estate professionals acquire their digital files in these ways:

• Purchase through a software vendor-Major vendors of GIS software also sell digital and attribute data so that their clients can become operational as quickly and easily as possible. The largest vendors publish comprehensive catalogs on the data they offer, e.g., "Conquest MarketData Catalog" from Strategic Mapping and "ArcData" from ESRI. Among the advantages of purchasing digital data from the GIS vendors are that the data is assured to be compatible with the vendor's GIS software, and maps will all be using the same cartographic projection system and coordinate system, and convenience. Disadvantages include GIS vendors not offering sources that a given user would prefer, and GIS vendors sometimes charging premium prices (not unlike a doctor prescribing an expensive "name" drug when an inexpensive "generic" drug might be equally effective).
   
• Purchase from a private sector data vendor-Private sector vendors usually bundle digital data with attribute data, e.g., the user receives census tract boundaries with the purchase of a sufficient number of variables on those census tracts (current and projected population, households, per capita income, number of houses in various price ranges, etc.). A compelling reason for this is that digital data does not change very often, but attribute data changes frequently, and so the vendor is mainly interested in repeat sales of attribute data. Most of the principal providers of digital data offer their products both directly to the public and indirectly through one or more of the above-described GIS vendor data catalogs.
   
• Purchase from a public agency-The leading sources of digital data are federal agencies, notably the United States Geologic Survey (USGS) and the Department of Commerce. Many if not most of the digital files sold by private sector vendors consist of repackaged and enhanced federal data bases; notable examples include the census tracts, census block groups, and street networks for all cities in the nation. At the state and local levels, government agencies vary widely in their willingness and ability to sell digital files of, say, all the assessor parcels in a community. Technical issues are secondary to political and legal issues, including freedom of information, warranties and liabilities, confidentiality and right to privacy, government entities competing with private companies, and so on. Though the number of local government agencies offering digital data to the public is increasing daily, the debate over policies, procedures and prices will continue to rage for some time to come in state houses, city council chambers, and court rooms throughout the nation.
   
• Create the data base in-house-Sophisticated GIS packages encompass digitizing capabilities so that users can convert hard copy maps into proprietary electronic files. Digitizing is labor-intensive and expertise-intensive, and therefore expensive. The vast majority of real estate professionals will not and probably should not learn how to digitize. If custom maps are needed (e.g., of submarket boundaries unique to a brokerage firm), outsourcing the digitizing to a service bureau is usually the better alternative.

In the near term, real estate professionals will acquire data in the above order; that is, buying data from the GIS software vendor will be the most frequent approach, followed by purchases directly from data vendors, and so on. Within a year or so "data stores" will begin popping up in cities around the nation for one-stop shopping of whatever data one needs in a given geographic area. Shortly thereafter, as data becomes more and more of a commodity, data catalogs will begin arriving in the mail much like the catalogs of MacWarehouse®, Egghead Software®, and other discount computer supply houses.