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MIGDIST1
Distance between counties, 1 year
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Description

MIGDIST1 is a constructed variable that reports the distance, in miles, between counties of residence, for sample-line, inter-county migrants for whom place of residence one year ago was ascertained.

The calculated distance in MIGDIST1 is the number of miles between the counties' 1970 centers of population. The latitude and longitude of the points were used in the following formula:

MIGDIST1 = 69.055 * ACOS [(SIN(LATA) * SIN(LATB)) + (COS(LATA) * COS(LATB) * COS(LONA - LONB))]
where:

LATA = latitude of 1949 county
LONA = longitude of 1949 county
LATB = latitude of 1950 county
LONB = longitude of 1950 county