When a historic district is first evaluated, the properties within the district boundaries are identified as either contributors or non-contributors. Contributors are the properties that date to the district’s period of significance and still retain enough of their historic character to convey the district’s historically important character. In contrast, non-contributors are not closely connected to the district’s significant historic qualities. This might be because they were built outside of the period of significance, or they may have been altered so much that have lost their connection to the district’s significance.
The number and arrangement of contributors within a district can vary from example to example. In some cases, a district with many non-contributors can still qualify for listing in a historic register, so long as the contributors that do exist are able to convey the district’s significant historical or architectural character.
In addition to contributors, districts have character-defining features. Character-defining features are the physical elements contributors share that allow them to express the district’s significance. Character-defining features can include elements like building and roof forms, exterior materials, window and door patterns, setbacks and lot placement, and landscaping.