A geographic area which has undergone past modification by human design or use in an identifiable pattern, or is the relatively unaltered site of a significant event, or is a natural landscape with important traditional cultural values could be a historic landscape. If the modifications, event, or values are over 50 years old, and the landscape possesses both significance and integrity in accordance with National Register criteria, the landscape may be eligible for the National Register. Not all possible landscapes will be found eligible or even require a full landscape study, however. Any geographic area which possesses a notable human relationship with the land and tangible physical features might be considered a cultural landscape of some sort, but many lack qualities which could possess the potential for historical significance. Landscapes with virtually no potential for eligibility because of age, lack of any significant associations, or substantial loss of integrity can usually be dismissed from consideration in a brief statement without conducting a formal evaluation. Generally, only identifiable landscapes over 50 years old which possess some level of significance and integrity will require a full formal evaluation to determine eligibility.

Robert Z. Melnick’s study, Cultural Landscapes: Rural Historic Districts in the National Park System (1984), was the first formal introduction of historic landscapes to the National Park Service. Melnick (page 8) provided a useful definition and identification guide that would apply to many landscapes:

In the early 1980s, the National Park Service identified four types of historic landscapes: sites, vernacular landscapes, ethnographic landscapes, and designed landscapes. For the purposes of cultural resources survey identification, landscapes can now be divided more simply into two basic types: designed (consciously created to reflect a design theory or aesthetic style) or vernacular (developed or evolved through function or use), by answering the question of why a landscape looks as it does. Sites and ethnographic landscapes can be identified as a subset of either a vernacular or a designed landscape.

The definitions of the four original NPS types can be useful in the process of identifying and analyzing a resource.

• Historic designed landscapes present a conscious work of creation. They were designed or laid out according to design principles or in a recognized style or tradition and may be important in the field of landscape architecture. Aesthetic values play a significant role in assessing designed landscapes. Designed landscapes are typically recognizable and fairly straightforward to evaluate. They may come with written documentation, even original plans and date of construction, or they may have been created on-site, by a nonprofessional, without drawn plans. In either case, a designed landscape should represent an important principle, theory, or style of landscape design. Integrity can be judged by reference to original design, noting intrusions and missing elements, keeping in mind the dynamic nature of living vegetation. National Register Bulletin 18 provides specific guidance on designed landscapes. Examples include formal gardens, cemeteries, parkways, and planned communities.
• Historic vernacular landscapes have evolved through use. They have been shaped by human activities or occupancy and reflect the physical circumstances and cultural character of daily lives. They generally contain large acreage and a proportionately small number of buildings and structures. Agricultural landscapes tend to dominate discussions of vernacular landscapes, but mining districts, industrial complexes, and transportation networks can also be historic vernacular landscapes. In general, vernacular landscapes have often proven challenging to recognize and evaluate. Without an original design plan for comparison, often lacking distinct boundaries or a defined local identity, they may blur into the surrounding background. These properties tend to occur relatively often and can present the most difficulties in survey work; consequently, much of the following material focuses on identification and evaluation of vernacular landscapes. Essential additional guidance on rural historic landscapes can be found in National Register Bulletin 30. Examples include agricultural areas, industrial complexes, transportation networks, and mining landscapes.
• Ethnographic landscapes contain natural and cultural resources that people associated with these features define as heritage resources. Although they must consist of tangible properties, these landscapes may possess significant intangible qualities more likely to emerge in the course of conducting research and interviews and less easily recognized on the ground. National Register Bulletin 38 provides guidance on traditional cultural properties which may qualify as ethnographic landscapes, such as contemporary settlements, sacred sites, and important topographic features. These landscapes can also include individual components, such as small plant communities or ceremonial grounds.
• Historic sites are significant for association with a historic event, person, or activity, where the location itself possesses historic, cultural, or archeological value. They are usually small-scale, relatively simple landscapes, although substantial archeological resources or extensive areas where historic events occurred may cover larger areas. They can be either designed or vernacular in origin, either individual landscapes or components of larger landscapes. In addition to archeological sites, they include places associated with important events or individuals, such as a battlefield, birthplace, or ceremonial site.

A historic landscape may include a grouping of resources such as topographic features, vegetation, water features, buildings, structures, objects, and sites. Designed landscapes and historic sites can be small, while rural vernacular landscapes are usually larger. In contrast to historic districts composed of concentrated built resources, historic landscapes typically extend over a wider area, contain substantial areas of vegetation or open space, and may also contain natural features that embody significant historical values.

To determine whether to view a property as a potential historic landscape or as a historic district, consider the role of open space and vegetation, arrangement of resources, property types, and visual character. A historic landscape will generally contain substantial areas of open space and vegetation, and often a variety of property types, combined in significant patterns or linkages. In contrast, a potential historic district is likely to have properties that are located closer together, without large areas of open space or vegetation, and may consist of relatively few or closely connected property types. Thus, a housing tract composed primarily of residential properties and minimal open space or an early freeway encompassing only highway-related resources within the right of way would be more likely to be considered as potential historic districts, while a large military base, public park, or broad transportation corridor might be looked at as possible historic landscapes. An estate or village with a compact core of structures surrounded by associated fields or pastures and parkland might be classed as a historic district with a landscape component within the district. It must be remembered that there is no clear-cut dividing line between historic landscapes and historic districts, and professional judgment should determine which category best recognizes the resource’s values.