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Digital Boundary and Annexation Survey (BAS) FAQs and Tips

Can I just send in my boundary?

We cannot accept or process submissions that only show the entirety of your boundary. The goal of Digital BAS is to update our geographic database according to the differences and/or changes between the Census-provided Shapefiles and your local data. Those differences and changes should be reported as individual polygons that are coded according to the instructions found in the Digital BAS Respondent Guide. Individual change polygons allow us to process changes to our database in a uniform manner, while also providing us with all of the required information needed for legal changes and boundary corrections.

What specific Census Shapefiles do I need to use for BAS?

We recommend using the following Census-provided Shapefiles regardless of the level of geography being reported for: edges, place, mcd/ccd, county, and water. If you are providing changes to Area Landmarks and/or Point Landmarks, those Shapefiles should be used as well (arealm and pointlm).

Are there step-by-step instructions on how to create a Digital BAS submission?

There is no single accepted method to create a Digital BAS submission using GIS. We recognize that users possess a wide range of experience and expertise in GIS, which allows a person to create a submission in many different ways. However, we do have a recommended 'example process' located in the Appendix section (Appendix 3A) of the Digital BAS Respondent Guide. While this section does not replace the detailed information within the respondent guide, it can be a good place to start reading to determine what data is needed, how to set up your files, how to create change polygons, and how to submit changes to the Census Bureau.

Do I need to return the BAS form (BAS-1, BAS-2, BAS-3, or BAS-5) with my digital response?

No. The information normally gathered on the forms will be extracted from the returned files. If any additional information is needed, you will be contacted.  We do request that you include a text or Word file with your contact information or use our online Annual Response Form. The 2015 BAS forms only include 2014 BAS annexations, for all annexations please go to Annexation Data.

Do I treat old legal boundary changes that were never previously reported to BAS as annexations/deannexations or boundary corrections?

If a legal boundary change appears to have never been reported (regardless of effective date), report it as an annexation/deannexation. If the change is just a correction to the way we have the boundary currently depicted (these should maintain the general shape of the boundary), report it as a boundary correction. If you are not sure, treat it as an annexation/deannexation and provide the documentation number and effective date.

I just ran Symmetrical Difference (or Union) as suggested and have a large number of polygons after exploding them. Is this normal?

Yes, this is not unusual. If this is the first time submitting changes through the Digital BAS method, you will see hundreds or thousands of change polygons. The large number of polygons is due to the fundamentally different spatial arrangement of linear features in Census TIGER data versus your local file, and may be aggravated by several years of paper map updates of boundaries during BAS. Please review the polygons per the Digital BAS Respondent Guide.

How do I submit my changes to the Census Bureau?

Changes should be submitted through the Secure Web Incoming Module (SWIM) site as outlined in the Digital BAS Respondent Guide. materials. Accessing SWIM requires the registration token that was emailed to the BAS contact 5 days after Responding Online. The subject of the email is “SWIM Registration Token”.

How do I get a SWIM token?

The BAS contact is emailed a SWIM token 5 days after the entity responds to the survey.

If you just downloaded Shapefiles and did not notify us, please Respond Online and the BAS contact will be sent a SWIM token in 5 days. In that time, please review your response by referring to the respondent guides to ensure your submission is in the correct format.

Respondent Guides

What is my 11-digit BAS ID?

BAS IDs can be found here: BAS Codes

What do I name my changes Shapefile(s)?

The naming convention list for all Shapefiles can be found in the Respondent Guide. The zip folder with Shapefiles should be named ‘bas<yy>_<basID>_return’ (for example: bas15_10100012345_return).

What is Consolidated BAS (CBAS)?

To reduce the burden on local governments and avoid duplication of efforts, the Census Bureau offers consolidation agreements to counties that are interested in submitting boundary changes for the legal governments (incorporated places and minor civil divisions) within their jurisdiction. The Consolidated BAS (CBAS) program allows counties to report boundary and feature changes for some or all of the legal governments within their county.  Once a local government agrees to the consolidation, the local government will no longer receive BAS materials.  Instead, the county BAS respondent will be responsible for providing the Census Bureau with all boundary updates.

For more information, visit the CBAS page.

I am a county respondent, what changes am I responsible for submitting?

As a county respondent, we are asking you to review and update your county boundaries as needed. However, most county respondents also report changes for the legal governments (incorporated places and minor civil divisions) within their jurisdiction. This is especially true for Digital BAS county respondents, where GIS data may be maintained by the county. Some counties have entered into a Consolidated BAS (CBAS) agreement with those governments, which states that the county will be responsible for reporting changes for all (or a portion of) governments within the county, reducing duplication of effort.

For more information, visit the CBAS page.

I have a legal change that is effective after January 1st. Should I go ahead and include that in my changes, or wait until next year’s BAS?

Go ahead and include all of your legal changes. We will process them according to the effective date in the attribute table. Legal changes that are effective after January 1st will not be processed for inclusion in the current year’s Census programs (such as the Population Estimates Program and American Community Survey). They will be processed at a later time in order to be included in the following year’s BAS products.

When will my changes be reflected?

This depends on the type of changes you submit, when you submit them, and (for boundary corrections) the number of changes in your submission. Any legal boundary changes which are received by the deadline of March 1st and were effective by January 1st of the same year will be reflected in the products from the same year's American Community Survey (generally this data is available in July of the same year). All legal boundary changes received after March 1st but before May 31st will be reflected in the next year’s BAS products. Boundary corrections and feature changes will generally all be reflected in the next year’s BAS products, but if you submit a very large file with many boundary corrections or features changes, we cannot guarantee that all of them will be reflected. In that case, any remaining boundary corrections and feature changes will be processed as time and resources permit. The Census Bureau appreciates your understanding and support in this matter.


Source: U.S. Census Bureau | Geography | (301) 763-1128 |  Last Revised: December 15, 2014