ZIP Code Tabulation Areas (ZCTAs) "are generalized area representations of U.S. Postal Service (USPS) ZIP Code service areas. They represent the most frequently occurring five-digit ZIP Code found in a given area. Simply put, each ZCTA is built by aggregating 2010 Census blocks, whose addresses use a given ZIP Code."

The boundaries of ZIP Codes and census tracts often don't match. If looking up which census tracts relate to a single ZIP Code, that overlap of boundaries doesn't create a major problem in terms of relative social and economic characteristics, but the counts won't be precise. If the analysis is being done for a larger area than a single ZIP Code, then just add up the data directly from the census tracts rather than converting their data to ZIP Codes.

Don't add up the ZIP Code data by allocating all of the data for each census tract to each ZIP Code which overlaps with each census tract and then summing the results; many of the census tracts would be counted multiple times unless additional steps were taken to deduplicate them. The example below shows the results for all of the ZIP Codes in Lake County, Florida; each of the Lake County census tracts in red appears in more than one ZIP Code (0301.02 would be counted five times). Instead, leave ZIP Codes out of the calculation and just add up the data for the selected area by census tract.

• 32102 - 0301.02 (plus 1 external tract)
• 32134 - 0301.02 (plus 9 external tracts)
• 32159 - 0304.07, 0304.08, 0304.09, 0304.10, 0304.11 (plus 4 external tracts)
• 32195 - 0304.11 (plus 2 external tracts)
• 32702 - 0301.02, 0301.04, 0301.05 (plus 1 external tract)
• 32720 - 0301.02, 0301.06, 0301.07 (plus 13 external tracts)
• 32726 - 0301.05, 0302.03, 0302.04, 0302.06, 0302.07, 0302.08, 0302.09, 0308.07
• 32735 - 0302.07, 0303.05, 0303.06
• 32736 - 0301.05, 0301.06, 0301.07, 0301.08, 0302.03, 0302.06, 0309.02
• 32757 - 0302.03, 0308.07, 0309.02, 0309.12, 0309.13, 0309.14, 0310.00 (plus 2 external tracts)
• 32767 - 0301.02, 0301.07
• 32776 - 0301.08, 0309.02 (plus 2 external tracts)
• 32778 - 0303.08, 0307.02, 0308.03, 0308.04, 0308.05, 0308.06, 0308.07, 0310.00
• 32784 - 0301.04, 0301.05, 0301.07 (plus 1 external tract)
• 34705 - 0310.00, 0313.01
• 34711 - 0312.02, 0312.04, 0313.05, 0313.06, 0313.07, 0313.08, 0313.09, 0313.10, 0313.11
• 34714 - 0312.02, 0313.11 (plus 1 external tract)
• 34715 - 0312.04, 0313.01, 0313.07, 0313.09
• 34731 - 0304.05, 0304.06, 0304.07, 0305.04, 0306.01
• 34736 - 0311.01, 0312.02, 0312.03, 0312.04, 0312.05, 0313.11
• 34737 - 0311.02, 0311.03, 0313.01
• 34748 - 0303.02, 0305.02, 0305.03, 0305.04, 0306.01, 0306.02, 0307.01, 0307.02, 0311.01, 0311.02, 0312.03, 0312.04
• 34753 - 0312.03, 0312.04, 0312.05
• 34756 - 0313.01
• 34762 - 0311.01, 0311.02
• 34787 - 0313.06, 0313.07, 0313.08 (plus 6 external tracts)
• 34788 - 0303.02, 0303.05, 0303.06, 0303.07, 0303.08, 0307.02
• 34797 - 0311.02