Methodology used Congressional Districts to ZIP

Hi Cole, Thank you for your post! There are a few additional considerations when working with data at the ZIP Code level or when working with Congressional Districts, which are currently created from ZIP Code level data. ZIP Code File Estimation- Because data collection at the ZIP Code level is not as complete additional assumptions are applied to ZIP Code file estimations. http://implan.com/index.php?option=com_content&view=article&id=590:590&catid=245:KB4 Understanding ZIP Code files - 9 considerations of ZIP Code and Congressional District files. http://implan.com/index.php?option=com_content&view=article&id=588:588&catid=245:KB4 Please let us know if you require additional documentation.

Thank you for the response, I am aware of the caveats and additional assumptions of the ZIP code areas and that CDs are built from ZIP codes. What I'm asking for is how, exactly, the IMPLAN programmers define aggregate ZIP code areas to make CDs. Thank you for your help.

Hi Cole, I again apologize for the delay of our response. We get our list of zip-codes that belong to each CD from Election Data Services. However, this list only includes ZCTAs, not point zip codes. Therefore, we have to search online for the Congressional District that each of those point zip codes belongs to. Thanks!

Thanks for the response. How does IMPLAN (what's the method), for example, apportion employment from zips to CDs since Congressional Districts and ZIP codes do not line up perfectly?

Hi Cole, We use a straight ratio. E.g. if a zip code falls into two Congressional Districts, we split it half and half. However, this doesn't happen often though. I hope that this helps! Thanks!