(Roger K. Lewis/for The Washington Post)

When you think about Washington’s most memorable physical attributes, you probably visualize iconic structures: the U.S. Capitol and the White House; the Washington Monument; and the Jefferson and Lincoln Memorials.

The neoclassical ensemble of Federal Triangle architecture, numerous museums and the city’s uniquely horizontal, low-rise skyline may come to mind. Or you may picture Victorian rowhouse facades lining streets in Capitol Hill, Georgetown or Adams-Morgan.

Decade after decade, books appear that are full of wonderful photographs, drawings and sometimes detailed descriptions of Washington’s architectural legacy. No wonder that the city’s edifices dominate imagery recall.

But you might be among those who focus on and remember something else: the form, quality and amount of public parkland and urban spaces around and between the city’s iconic structures, or threading through the city’s fabric. For some people, Washington’s landscapes are no less memorable than its architecture. And maintaining landscapes can be just as challenging and costly.

Landscape designs and landscape experiences in the nation’s capital are incredibly numerous and diverse. Yet appreciating them requires paying attention to each site’s unique attributes, some changing with the season. Landscape characteristics include site shape and topography; pathways, paving patterns and textures; trees, shrubs, flowers and ground covers; water features; and landscape structures, such as colonnades, pergolas, fences and walls.

To help local citizens and millions of annual visitors explore, understand and better appreciate the city’s landscapes, and not just its buildings, the American Society of Landscape Architects (ASLA) recently launched its “Landscape Architect’s Guide to Washington, D.C.” The online guide is “mobile-friendly” ( www.asla.org/guide ) and comprehensive. With more than 800 photographs, it documents 76 sites in D.C. and Arlington. The 76 sites are within 16 distinct geographical areas, and each area constitutes a potential tour.

Twenty experienced landscape architects worked with the ASLA to select these historic and modern landscapes. Acting in effect as individual online guides, they wrote descriptions and commentaries to explain each site from a landscape architect’s point of view. The goal was to show how design influences the way people interact with or even feel about a site.

The guide identifies many iconic, well-known sites associated with memorials, monumental buildings or landmark urban locations, such as the World War II Memorial and the National Cathedral. Some sites — Rock Creek Park, the National Zoo, Kenilworth Park and Aquatic Gardens — are natural parklands. One of the 16 places in the guide is not really a site, but rather D.C.’s bicycle network.

A number of areas are outside the city center. And a few were selected in part because they embody and exemplify state-of-the-art landscape sustainability techniques and green infrastructure strategies such as water-cleansing wetlands, bioswales and pervious paving.

The most familiar of the 16 areas are the Mall, the White House and Pennsylvania Avenue. These three areas encompass 25 distinct sites. Among them are landscapes surrounding each national memorial; Constitution Gardens; the Hirshhorn Sculpture Garden; the Tidal Basin; the Ellipse and Lafayette Park; and Pershing Square Park, Freedom Plaza and John Marshall Park, in addition to Pennsylvania Avenue itself. Like parks, streets are seen and understood as designed landscapes.

The guide cites L’Enfant Plaza, Navy Yard, Chinatown and NOMA as areas with landscaped sites worth looking at. Capitol Hill encompasses nine landscaped sites, ranging from the Capitol Building’s west grounds to Eastern Market and Congressional Cemetery. Among Georgetown’s eight sites are the Potomac River waterfront park; the C & O Canal and Cady’s Alley; Georgetown University; Dumbarton Oaks and its park; and the Oak Hill Cemetery.

Areas a bit farther out include Dupont Circle, Embassy Row, Columbia Heights, Shaw, Adams-Morgan, Brookland, Woodley Park and Anacostia.

Sites described in the guide’s 16th area — Arlington/Pentagon/Rosslyn — are all memorial landscapes: Arlington Cemetery, Arlington Memorial Bridge, the Women in Military Service for America Memorial, the Pentagon Memorial, the Air Force Memorial and the U.S. Marine Corps War Memorial.

Keep in mind that it’s not architecture that the guide seeks to highlight. Rather, attention is focused on landscapes in which architecture is situated, on public spaces framed or anchored by architecture. The ASLA hopes people will realize how much the visual composition and emotional power of the Lincoln and Jefferson Memorials, for example, are tied to and depend on their extraordinary landscape settings and the elements comprising those settings.

Perhaps using the ASLA guide and paying more attention to the city’s landscapes will reveal one other critical landscape attribute: the amount of investment, care and maintenance required to create, nurture, preserve and sometimes enhance the city’s wealth of beautifully landscaped environments.

Roger K. Lewis is a practicing architect and a professor emeritus of architecture at the University of Maryland.