Data Best Practices

Following is a series of best practice for data collection and file creation and suggestions about best practices of formatting data within your VIP XML and CSV file.

Naming convention

While many of the Voting Information Project’s data processes are managed by software, the quality of the entire system relies on human intervention, especially for error reporting and quality control. For this reason, VIP files should follow a naming convention that describes the contents of each individual feed file in an accessible way.

The file containing the VIP feed should be named using the following convention:


An explanation of each of the segments of the file naming convention above are as follows:

  • ${FIPS} - The FIPS code for the jurisdiction.

  • ${ELECTION_DATE} - The date of the election in ISO 8601 format.

  • ${STATE} - The full state name (e.g. Alaska, Arkansas, etc…) and not the abbreviation. If there are spaces in the state name, they should be substituted with underscores (e.g. New York -> New_York).

  • ${LOCAL} (optional) - This additional identifier should be used if the file contains data from a specific jurisdiction. As with ${STATE} above, all spaces should be substituted with underscores. For example, if the data contained in the file only covers Maricopa County, AZ for the November 6, 2012 election, the file name would be vipfeed-04013-2012-11-06-Arizona-Maricopa_County.xml.

  • {xml|zip} - If the file is an uncompressed XML document, the extension should be .xml. If the file is zipped, the file extension should end with .zip.

For a final example, denotes Iowa’s (NB: the FIPS code for IA is 19) feed for the Nov 6, 2012 election that has been compressed.

Element Identifiers

Most elements within the VIP feed require unique identifiers, xs:ID data types. Conformance to xs:ID requires the identifying record to:

  • begin with a letter or underscore

  • only contain letters, digits, hyphens and periods

  • be unique across the VIP data set

In order to maintain uniqueness and provide context for the identifiers, the best practice is to use Hungarian-Style notation for identifiers.

ID values should follow Hungarian-Style notation, were the identifier prefix implicitly names the data element. Below is a list of preferred prefixes by element (e.g. par00001 for a Party id):

















































File Structure

All XML and CSV files should be encoded UFT-8 and line breaks should be LF (\n) as opposed to CR LF (\r\n).

For consistency across files and to aid human readability all indentation of elements should be an indent of two spaces and tabs should not be used. Each child node of an element should also be indented an additional two spaces.

General Data Structure

All data that are presented to end users of the data (i.e. contest names, referendum text, polling location names, street names, proper names), where possible, should be converted to Title Case to aid readability.

All data should be trimmed to remove leading and trailing white space.

Optional elements without values should be omitted from XML feed.

Specific Data Types

Elements with a data type of xs:integer must contain a valid whole number greater than zero.

Elements with a data type of xs:anyURI should be entered as a fully qualified domain name (e.g.

Elements with a data type of xs:dateTime should be entered in ISO-8601 format.

Elements with a data type of xs:boolean should either have a value of true or false

Elements with a data type of xs:language should contain a two character, lower-case, value corresponding to the ISO 639 standard.

Elements that have enumerations which include an other should have a corresponding value assigned to OtherType within the containing element. For example:

 1<BallotMeasureContest id="bm390616670907">
 2   <BallotSelectionId>bms390616670907</BallotSelectionId>
 3   <ElectoralDistrictId>ed3906177703103</ElectoralDistrictId>
 4   <Name>Proposed Tax Levy School District</Name>
 5   <SequenceOrder>34</SequenceOrder>
 6   <FullText>
 7     <Text language="en">An additional tax for the benefit of the Lockland Local School District, County of Hamilton,
 8     Ohio, for the purpose of CURRENT EXPENSES at a rate not exceeding eleven and two-tenths (11.2) mills for each
 9     one dollar of valuation, which amounts to one dollar and twelve cents ($1.12) for each one hundred dollars of
10     valuation, for a continuing period of time, commencing in 2015, first due in calendar year 2016.</Text>
11   </FullText>
12   <SummaryText>
13     <Text language="en">4 Proposed Tax Levy</Text>
14   </SummaryText>
15   <Type>other</Type>
16   <OtherType>bond</OtherType>

Specific Data Elements

Street Segments: Valid street segment records should not contain leading zeros in xs:integer fields and should have a Zip value of 00000 if a value is unknown.

External Identifiers: External identifiers with an enumeration of fips should contain valid FIPS code values as defined by the U.S. Census Bureau. External identifiers with an enumeration of ocd-id should contain a valid Open Civic Data Division Identifier.

For long text fields (e.g. FullText in BallotMeasureContest) the XML line break (&#xA;) should be used to enforce line break styling.

In all fields the characters <, >, and & should be encoded &lt;, &gt;, and &amp; respectively.

Geospatial Data

The following sections provide guidance and best practices on using geospatial data with a VIP feed. Geospatial data represents the geographic modeling of a shape on the Earth’s surface (i.e. a polygon on a map), and within the context of a VIP feed is primarily used to model the boundary of voter precincts. In places where voter precinct shapes are available, this capability is intended to be straightforward and lightweight to integrate with existing GIS tooling.

Geodetic Datum

VIP exclusively uses the 84 revision of the World Geodetic System (WGS 84) as the geodetic reference system by which geospatial coordinates are defined. This applies to geospatial coordinates provided within the VIP feed itself (e.g. PollingLocation.LatLng) as well as coordinates provided in an external geospatial file.

Assigning Voters to Precincts

Voter precincts are the atomic unit of electoral districts in the U.S., and provide the mechanism by which voters are mapped to their polling places, ballot information and more. It is critical that voter locations are mapped to the correct precinct in a VIP feed in order to provide the most accurate and reliable voting information.

There are two mechanisms by which voters can be assigned to precincts in a VIP feed:

  1. Street segments

    A voter address that maps to a street segment is assigned to the precinct given by StreetSegment.PrecinctId. This is the traditional approach of assigning voters to precincts that has been in use since the beginning of the VIP specification.

  2. Containment within a precinct boundary

    A geocoded voter address that is contained within the geographic boundary of a precinct is considered assigned to that precinct. The geographic boundary of each precinct is defined by Precinct.SpatialBoundary. This is a newer approach of assigning voters to precincts that was supported starting with version 6.0 of the VIP specification. Compared to the approach of using street segments, geospatial data offers a far more accurate and reliable solution to mapping voters to precincts, and thus should be the preferred approach whenever possible.

Providing both street segments and precinct shapes

There are some cases where precinct boundaries alone are not sufficient to accurately map all voters to their precinct. For example, if a precinct boundary divides an apartment building, there is no way to distinguish the correct precinct for voters that live in this building using a two-dimensional shape on a map.

To mitigate this limitation of geospatial data, it is possible to provide both street segments and precinct shapes in the same VIP feed. If a voter’s location is determined to map to a street segment and is also contained within a precinct shape, the precinct assignment from the street segment will be preferred.

Using the above example where a precinct boundary runs through an apartment building, this scenario could be handled by providing street segments in the VIP feed, in addition to precinct shapes, to specify the mapping of apartment numbers to precinct. For N apartments in the building, there could be N street segments provided in the feed, each with a distinct StreetSegment.UnitNumber and precinct assignment. If a voter address maps to one of these street segments, the precinct assignment from the segment will supersede a precinct assignment given by containment with a precinct shape.

Exporting and packaging geospatial files with a VIP feed

Geospatial data files are provided in a native geospatial format. Each geospatial file should adhere to standard industry conventions and requirements of the corresponding GeospatialFormat. In most cases, these files will be exported directly from a GIS tool or an Election Management System and delivered alongside a VIP feed.

All referenced external files need to be packaged with the VIP feed file, and archived together within a single ZIP file. The following is an example of the file structure for the case of an XML feed file that includes ESRI shapefiles.

Example file structure:


    • vipfeed-19-2012-11-06-Arizona.xml


      • precinct_shapes1.shp

      • precinct_shapes1.shx

      • precinct_shapes1.dbf


      • precinct_shapes2.shp

      • precinct_shapes2.shx

      • precinct_shapes2.dbf

The expected file type and structure of each individual geospatial file will depend on the GeospatialFormat being used. The external file referenced from the VIP feed may be a flat file, but it could also be a ZIP file containing multiple relevant files, as the geospatial format requires. The following provides geospatial data file requirements by format.

Expected file type and structure by Geospatial Format:


Expected file type


shp (ESRI shapefile)


The referenced external file should be a ZIP archive containing, at a minimum, all files required by the ESRI Shapefile f ormat. The filename referenced from the VIP feed should be the name of the ZIP archive for the shapefile. Required files within the archive include a main .shp geometry file, a .shx index file, and a .dbf attributes file. Other optional files as part of the ESRI Shapefile specification are permitted, but may be ignored.

Individual files within the shapefile archive are identified by file extension. For example, the main geometry file is identified by the file within the archive with a .shp file extension, regardless of the file name. It is therefore required that there is only one file per expected file type within the archive.

Referencing specific shapes within a geospatial data file

Geospatial data files will usually contain many shapes. For example, depending on how the source shape data is managed, it may be easiest to export a single file containing all precinct shapes represented in the VIP feed. A precinct boundary is modeled in the feed as a reference to the external geospatial data file, but in most cases only one or a few shapes contained in that file are relevant to the precinct.

The specific shape(s) within the external file that comprise the spatial boundary of the geometric feature are captured by the field ExternalGeospatialFeature.ShapeIdentifier. ShapeIdentifier is a repeated string field, but the expected value will depend on the geospatial format of the external file. For example, an integer type is expected when using the ESRI shapefile format, so the string value of ShapeIdentifier should be parsable as an integer.

Expected type of ShapeIdentifier by GeospatialFormat:


ShapeIdentifier expected type


shp (ESRI shapefile)

32-bit integer

ShapeIdentifier should be parsable as a 32-bit integer. Geometric features in an ESRI shapefile are ordered in sequence, and the ShapeIdentifier value corresponds to the zero-based index of a record within the file. For example, a ShapeIdentifier value of “35” is a reference to the 36th sequential record in the shapefile.

External file checksums

Geospatial data is provided in the form of supplemental files external to the VIP feed itself. Since this effectively divides the full set of information of the feed across multiple files, it’s essential that references between files be reliable. This is ensured by verifiable cryptographic checksums.

Each external file reference includes the name of the file and its checksum. A checksum includes both the raw cryptographic hash of the file’s contents, as well as information about which cryptographic algorithm was used to compute the value. A consumer of a VIP feed should be able to compute a checksum value of an external file using the same algorithm and independently verify it matches the checksum value in the feed.

It’s worth noting that having a file checksum also introduces an opportunity for consumers of the data to optimize their processing of it. If the contents of a VIP feed are updated, but the checksum for an external geospatial data file has not changed, then the consumer could omit having to reprocess the geospatial aspects of the feed.

Requirements for precinct shapes

The following are practical requirements when defining the spatial boundary of a Precinct element (whether a precinct or precinct split) with geospatial shapes.

  • The resolution of a polygon for a precinct shape can be as coarse or fine as needed, so long as the shape accurately represents the boundary of the precinct.

  • No two shapes should overlap.

  • All polygons must form a closed loop. That is, the polygon should start and end from the same point.

  • The border of a polygon must not intersect itself.

  • The spatial boundary of a Precinct is defined by a single geospatial feature. That feature, however, may contain one or more discrete and non-overlapping polygons as necessary to define the full extent of the boundary.

  • ShapeIdentifier must be a valid, existing reference in the external file.

  • ShapeIdentifier must have an expected type according to the table above.