# Using Crosswalk to transform 2005-09 ACS to 2010 Tract Boundaries **URL:** \ **Category:** NHGIS\ **Created:** [October 20, 2020, 6:41pm UTC](https://forum.ipums.org/t/using-crosswalk-to-transform-2005-09-acs-to-2010-tract-boundaries/3815 "2020-10-20T18:41:05Z")\ **Posts on this page:** 1\ **Showing post:** 2
**Author:** ![JonathanSchroeder](https://sea1.discourse-cdn.com/flex019/user_avatar/forum.ipums.org/jonathanschroeder/32/70_2.png) [@JonathanSchroeder](https://forum.ipums.org/u/JonathanSchroeder)\ **Post date:** [October 22, 2020, 3:56pm UTC](https://forum.ipums.org/t/using-crosswalk-to-transform-2005-09-acs-to-2010-tract-boundaries/3815/2 "2020-10-22T15:56:51Z")
There are a couple issues that will make your goal uniquely challenging… First, no ACS data are published at the block level, so you won’t _directly_ be able to use the NHGIS block-to-block crosswalks. We also recently added crosswalks for “block group parts,” the smallest units used in 1990 and 2000 long-form summary tables, but again, no ACS data are available for block group parts either. The smallest units identified in 2005-2009 ACS summary tables are for _block groups_, so I’d recommend you create a crosswalk from those. (Note: you say that you “will be using census tract level data”, but that doesn’t need to determine the level you start _from_; it often only determines the target level that you want to crosswalk _to_. As explained [on our crosswalks page](https://www.nhgis.org/user-resources/geographic-crosswalks#selecting), it’s generally best to crosswalk _from_ the smallest possible units. If you currently have the SES indicators only for tracts, it’s still likely you could obtain most or all them for block groups, too, which is worthwhile if you’d like the most accurate possible stats for 2010 tracts.) In this [previous forum post](https://forum.ipums.org/t/can-i-use-nhgis-crosswalk-for-block-group-level-data/2750), I describe how you can use the NHGIS crosswalks for data from block groups. The same principles apply in your setting. Second, as noted in the NHGIS [GIS Files documentation](https://www.nhgis.org/documentation/gis-data#years), the tracts and block groups identified in the 2005-2009 5-year summary tables generally correspond to the 2000 census definitions of these areas, but in 19 counties, they don’t correspond exactly to either the 2000 or 2010 definitions of tracts and block groups. This [Census web page](https://www.census.gov/programs-surveys/acs/technical-documentation/table-and-geography-changes/2009/geography-changes.html#par_textimage_2) provides more details, including a list of the affected counties. If you need data in any of these 19 counties, you’ll need to do additional research to determine how the 2005-2009 ACS data correspond to 2010 tract boundaries. --- _[View the full topic](https://forum.ipums.org/t/using-crosswalk-to-transform-2005-09-acs-to-2010-tract-boundaries/3815)._