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I set up Tiger Geocoder in PostGIS on my local box (PostGIS 2.1.3, PostgreSQL 9.3.5, Tiger 2013 data).

The problem I'm running into is that on almost every street most of the points are clustered, with only a few addresses in their correct locations. You can see an example in the image below:

Clustered Addresses

My first thought was that somehow I had set up the geocoder with the wrong SRID, but I did everything "by the book" and I have tried several times but I still get the same results.

Is this to be expected with Tiger data or am I doing something wrong?

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The documentation you are referencing (see the proposed answer below) from the Census Bureau's site refers solely to the Landview 6 product (released in 2003).

The Census Bureau does not release information about specific addresses, including the exact location, due to Title 13 of the US Code. The TIGER/Line Shapefiles and the Census Geocoder documentation both include information about the publicly available address ranges.

The geocoder takes the address and determines the approximate location offset from the street centerline. An interpolated latitude/longitude coordinate is returned along with the address range the Census Bureau has on that stretch of road. That coordinate is then used to determine the geography that the address is within.

Q. What is the source of your address ranges?

A. The address ranges used in the geocoder are the same address ranges that can be found in the TIGER/Line Shapefiles which are derived from the Master Address File (MAF). The address ranges are potential address ranges, not actual address ranges. Potential ranges include the full range of possible structure numbers even though the actual structures might not exist. The majority of the address ranges we have are for residential areas. There are limited address ranges available in commercial areas. Our address ranges are regularly updated with the most current information we have available to us.

http://www.census.gov/geo/maps-data/data/geocoder.html

  • Thank you! This clarifies what I'm seeing. I'm updating this as the answer. – John Sampson Sep 30 '14 at 14:48
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NOTE: Since I added this answer JLH has given a much better one, so please refer to his answer.

My original conclusion below:


I received no answers on this, so naturally I investigated it further myself.

My Conclusion: the Tiger data is precise enough to geocode to the correct street, but not to the actual lot.

I determined this after testing a good number of addresses on OpenStreetMap.org, which is also based on the Tiger data. The addresses were clustered in the exact same way as what I was seeing in my Tiger data.

The US Census Bureau says this about their data:

Due to resource constraints the enumerator updates were digitized directly into the Census TIGER data base without geodetic controls or the use of aerial photography to confirm the features' locational accuracy.

And this:

Changes made by local officials do not have geodetic control.

But the good news is:

The Census Bureau is currently in the early stages of developing a system to significantly improve the coordinate accuracy of features in the TIGER data base and to devise a more effective approach to updating features.

https://www.census.gov/geo/landview/lv6help/pos_acc.html

Worthy of note

A study on the Tiger data accuracy was done in 2009:

http://wiki.washjeff.edu/download/attachments/41946665/JGG_3574.pdf

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