Thursday, April 24, 2008

Neighborhood Change Database

This is a brand new Geolytics database that we have just purchased. It is highly specialized and essentially serves one purpose: it allows patrons to directly compare census tract data from 1970 to 2000 in tables and maps.

Manhattan Census Tracts

Census tracts are statistical units created by the Census Bureau. They vary in area and tend to be larger in rural areas and smaller in urban areas. They were designed to have a population between 1500 and 8000 people, with an ideal size of 4000. Census tracts nest within county and state boundaries and never cross these boundaries. They are ideal for examining change within counties and cities.

The problem with making historical comparisons is that census tracts change over time, which makes direct comparison difficult. Over time, a tract may be split into two new tracts (in areas of population growth) or two tracts may be aggregated into one (in areas of population decline). In some instances, boundaries may have to be redrawn entirely.

This databases accounts for this problem by normalizing the data. The tracts and the data from 1970, 1980, and 1990 have all been manipulated to fit the 2000 census geography. This allows for direct geographic comparison across the four decades (you would choose the All Years option under Counts to access the normalized data). You also have the option of viewing the data the way it looked when it was released by selecting the individual census years under Counts.

You use the database to build your own tract reports. You select the area of interest (tracts within a state or county), the census year(s) of interest, and specific variables. You can view the data in a table, which you can download and use in Excel, or you can view the data in a map, where you can download it as a shapefile for use in GIS. You can also right click on the map and save it as an image.

Currently, the database can only be accessed using the Internet Explorer (IE) browser. Firefox isn't able to process it. I don't know if it will work with Mac browsers or not.

For most census questions, you'll still want to refer patrons to the Census Bureau's website or the Social Explorer (in our DB list). The Neighborhood Change db is dedicated specifically to time series analysis for census tracts - and can be a little daunting to use. Perhaps we can do a demo in the future.

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