The word “graffiti” usually conjures images of people with spray cans illegally making murals or jotting down tags using colorful paints. A lot artistic interventions use other tools and materials, though, subverting expectations and working in (literal and legal) gray areas to create works without leaving a conventional trace. Consider, for instance, the massive deep sea monsters, jungle predators and swamp creatures of Russian illustrator Nikita Golubev that lurk in the grimy shadows on the sides and backs of trucks.

Along similar lines, this series of skulls by artist Orion was made by scrubbing car exhaust from an active tunnel. For those looking to deter street art and artists, subtractive interventions like these can be tricky to pin down. After all, Golubev and Orion are simply cleaning vehicles or public surfaces, albeit very selectively. In many cases, the end result is actually further cleaning — art like this often pushes municipalities to send out teams that then wash off entire areas to make them look consistent again.

This artistic approach draws different reactions depending on the scale and situation. Take snow calligraphy, for instance — few people seem to mind a nice message traced into the hood of their car. Artist Faust notes that virtually “everyone has an affinity for writing in the snow as a child,” so perhaps it’s also something people feel they can relate to on a more experiential level.

Reverse graffiti not only provokes different response—it also spans a variety of materials and methods and can work with greenery as well as it does with snow or grime. Some moss artists work additively, creating mixtures to apply to surfaces and thus encouraging moss to follow particular grown patterns to produce an specific result. Others, however, actively remove moss to create desired words, patterns and illustrations.

Stefaan de Croock falls into the latter category, using power-washing tools to create cityscapes and other whimsical scenes on surfaces previously covered in layers of moss. As with a lot of reverse graffiti projects, his pieces are generally temporary — the moss simply grows back in to fill the voids over time.

SpY’s work in Besancon, France, combines elements of reverse graffiti and tree sculpting. Turning topiary approaches into a mural-making technique, he shaped vines into a circular work of wall art using an elevated work platform, trimming his way toward a perfect circle.

Light art and projection bombing are even more temporary and generally even less invasive than reverse graffiti. Lighting machines aimed at buildings to create patterns or spell out messages can be targeted and disabled if they persist, but ephemeral light painting like the above work by Lichtfaktor are deployed quickly using glowsticks or other portable devices and have to be captured on camera to work, making them brilliantly elusive.

Meanwhile, if light art is about brief visibility, then hydrophobic spray art is about lasting invisibility. Both are made to be seen and not seen in particular ways, but the latter has a key ingredient that determines when a design or artwork is visible: wetness.

When the hydrophobic NeverWet spray came out, it promised to waterproof everything, but some users found they had mixed results in applying it to things like clothing and touchscreens – it discolored shoes and left a sticky film on devices. Then someone thought to create a stencil and tag sidewalks with the stuff and a new type of visible-when-wet graffiti was born. One can, of course, free-spray with it as well, but stencils help make the outcome more controlled and predictable.

The same basic artistic idea has been applied in other contexts by designers, too — selective hydrophobia can be incorporated into brick pavers or concrete sidewalks, for instance, to create patterns that change with the weather. Clever urbanists might consider ways to integrate useful messages or wayfinding elements into such projects, like arrows pointing to nearest sources of shelter in a storm. Similarly, messages that appear on surfaces that change color with temperature could be used to guide people on particularly hot or cold days.

Practical designs aside, artists continue to experiment outside of traditional material palettes with works that raise questions about visibility and invisibility. There is fun to be found at the intersections of these ideas, embodied in projects like this one by 3D artist Milane Ramsi, who combined different approaches into a single installation — a concrete pillar appears to vanish while simultaneously revealing three-dimensional lettering more reminiscent of conventional graffiti.

Additive or subtractive, vandalism has its grey areas, but what about the seemingly more straightforward removal of graffiti? Here again there are shades of gray. Some artists, like Mathieu Tremblin, paint a surface clean then write over graffiti with their own work — in his case: humorously replacing loose tags with digital-style tag clouds. That, clearly, is of a kind with what was underneath; in places where tagging is illegal, replacement tags are too.

Then there is the saga of the infamous Banksy and the so-called Gray Ghost, an anti-street artist who leaves signature splotches of gray in the wake of his graffiti removals. Some argue the Ghost’s work vandalizes art — others say it is itself art. Legally, like Banksy’s illegal murals, both artists work in a similar space, though in Banksy’s case building owners often go to great lengths to preserve his art, in part for its monetary value.

Exceptions aside, municipal laws are usually clear on painted public art and the goal is generally total graffiti erasure, though it doesn’t always work out that way. This kind of official cleanup usually draws binary responses, viewed by some as a welcome fix and by others as an act of defacement. One award-winning film, however, argues for a third point of view: graffiti removal as the ultimate next step in the progression of modern art. Despite its semi-satirical intent, The Subconscious Art of Graffiti Removal raises provocative questions about what constitutes street artwork in the gray areas of additive and subtractive graffiti.

In Newark, New Jersey, a large and deceptively nondescript building is redefining the Garden State, producing millions of pounds of food per year just outside of Manhattan. This 70,000 square foot facility has the equivalent yield of over 5 million square feet of traditional farmland. Inside, a year-round, closed-loop aeroponics system employs no pesticides and requires 95% less water than field farming. This branch of AeroFarms is not alone — it’s part of a food production revolution with projects ranging from at-home and in-store micro-farms to massive facilities set up in old factories and warehouses around the world.

Technically, vertical farming can be done outside, too, by stacking planters in natural sunlight, but indoor vertical farms offer a range of advantages. Inside, there are no seasons and specialized LED lights make it possible to grow plants continuously and cycle through various crops more easily. The controlled environment and standardization of these systems also makes automation easier. In Japan, approaches have gone predictably high-tech, with endeavors like the Vegetable Factory, which is operated entirely by robots.

Spatial containment makes recycling more efficient, mitigates spoilage and reduces the risk of diseases and pests spreading beyond a specific facility. Transportation costs and energy requirements are also reduced for farms that move into old factories and warehouses right in and around cities, putting them closer to consumers. Aeroponics in general also require less material input — mainly mist and air with minimal water and soil — leading to a lighter footprint.

What started in large and independent facilities has begun to spread into mainstream grocery stores and supermarkets, too. A few years back, Target started testing direct retail micro-farms, beginning with leafy greens before moving to tomatoes, peppers and more. Since these kinds of retail spaces are climate-controlled already for the sake of both shoppers and products, less added energy is required to maintain ideal conditions.

In Berlin, a company called INFARM recently partnered with local shops to provide similar in-store services, cutting down on farm-to-table distance right in the heart of a major European metropolis. Meanwhile, in Tokyo, vertical creepers, rice paddies and broccoli fields were integrated into the design of an otherwise Modern-looking office building, brightening up the place while also providing food for the employee cafeteria.

Taking vertical integration a step further, projects like the ReGen Villages aim to incorporate stacked farms directly into residential communities. It may sound impractical or even Utopian, but at its root the idea is relatively traditional: backyard gardens and community gardening are nothing new. Coupled with walkability and density, these kinds of green-centric towns have a lot in common with New Urbanist ideas that go back decades.

Still, it is generally wise to maintain a healthy skepticism when it comes to fresh green architectural trends and technologies and eye-catching renderings. Skyscrapers covered in greenery (or treescrapers), for instance, have proven to be popular but also problematic in practice (catchy conceptual earthscrapers, groundscrapers and sidescrapers, too, for that matter). Sometimes, more practical organic solutions are hiding in plain sight. Take wood, for instance, a historically popular green building material now finding new forms and reaching new heights in tall buildings around the world. Newer is not always better.

Some extreme vertical farming ideas may indeed prove to be far-fetched and unsustainable, but market movements suggest there is a future in these kinds of facilities and approaches. Investors are putting their money where people’s mouths are, buying up disused urban real estate and developing new indoor farming technologies. Already, vertical farming is a $2,000,000,000 industry and experts project it will grow as much as 30% per year over the next decade.

Vertical farms are of course not a complete solution to ongoing threats like climate change and mounting global food crises, but they do show promise — these endeavors are slowly breaking down urban and rural barriers, reconnecting cities with the food sources that sustain them and shortening that critical distance from farm to table.

Years ago in McAllen, Texas, an old abandoned 124,500-square-foot Walmart superstore was renovated and put to new use as the largest single-floor public library in the United States. Across America, many malls have emptied out and thousands of abandoned big box stores sit empty, including hundreds of former Walmarts. Some, though, are getting creative new leases on life, becoming community markets, indoor tracks, gaming spaces, museums and more.

In McAllen, aisles that used to divide shoppers have been adapted or replaced to serve the community. The old Walmart is packed with computer labs, public meeting spaces, a cafe, an art gallery, a used bookstore and more. In other small towns and suburbs around the United States, the generic promise of all-in-one convenience big box stores once offered is being realized in new and site-specific ways.

Designers at the research and development lab of KTGY Architecture + Planning in Los Angeles have particularly inspiring aspirations for old shopping centers: plug-and-play modular prefabs that subdivide big empty boxes into transitional housing for the homeless. This is not the first time architects and designers have attempted creative solutions to this pervasive problem, but it’s notably ambitious.

The firm’s Re-Habit project involves housing as well as support spaces and services fit into unused spaces in big boxes or individual shopping outlet stores like Sears and JCPenney. Self-supporting communal residences, where occupants rotate chores like working in the kitchen or keeping the dining hall clean, are coupled with facilities to providing training and potentially even employment.

Where some might see empty space, others see opportunity. The large, flat roofs of big box stores, for example, are ideal for rooftop gardening, open-air recreation and solar panels — these kinds of uses would pair well with a project like Re-Habit. Many big boxes have outdoor plaza areas (not to mention giant parking lots) that could accommodate small pop-up shops and food carts, too.

Adaptive reuse in the realm of big retail is forward-thinking but also proven concept. Big boxes have been turned into commercial gyms, corporate offices, schools, churches and (yes, this is true) even a SPAM Museum. Whatever the project, it takes vision and resources to turn such dauntingly huge structures around as well as an understanding of the potential pitfalls and unique opportunities of this peculiar building typology.

Such large-scale conversions tend to work best when they take advantage of big box assets and work within their limitations. Generally, big box stores reside in huge buildings that are located in prime spots, often along highways, which makes them accessible but can also make them hard to fill up. They generally have a lot in common, like orientations that lend themselves to being sectioned into bays and limited natural light, features that can work well for things like libraries. Often, though, the best option is simply whatever best fits community needs, which is often a mixed-use program that can more effectively fill out a bigger interior.

Big retailers may be more prevalent in suburbs, but there are some prime urban examples as well. A series of converted Sears plants in major US cities offer a range of realized visions for what big old commercial buildings can become. In Minneapolis, for instance, a massive mail-order Sears plant and retail store was abandoned by its makers for years before being turned into the Midtown Exchange, a busy structure full of restaurants, stores, offices, condos and apartments. It took a lot of players to make this work, including invested city officials and both public and private funding from various sources.

Often, these conversions speak to the character of the cities in which they are located. In Seattle, a place known for its coffee, the city’s old Sears plant now houses the Starbucks headquarters. In Los Angeles, land of Hollywood, a deserted Sears was used for film shoots during its derelict years but is on its way to becoming a residential and commercial hub. Boston and Memphis have converted Sears projects, too — uses are mixed in both cases.

While the individual projects vary, each city has something in common having turned a similarly monumental structure into something new. These various projects fill in gaps and address needs that are fundamentally local. Together, they represent a series of blueprints that other cities can look to, whether they have Sears plants themselves or are simply looking for ways to deal with big old commercial spaces.

Existing examples can provide paths forward, but other architects have grander visions, too, some of which have yet to be tried. Designers could, for instance, build around big boxes on all sides, then turn the central old structures into community hubs or parking lots or productive green spaces. Another option is to tear down sections of roofs and facades, dividing big boxes up into smaller and more manageable units while leaving structural supports intact.

There is no one-size-fits-all solution for disused spaces, but cities, towns and sururbs looking for inspiration have both real-world examples and conceptual designs to draw on. In some sense, the core recipe never changes — for any big transformation project, municipal officials, citizens, developers and designers will always have to come together to find best-fit solutions on a case-by-case basis.

Most cities have so much in common that a generic “map of every city” can seem similarly familiar to people living in London, Paris, New York or another metropolis entirely. General types of neighborhoods aren’t the only things different cities share, though — much less obvious but pervasive are sets of codes, symbols and markings that can communicate meaning across different times and urban spaces.

Even though (or perhaps because) people drive over and walk by them every day, it is easy to overlook the rich, colorful and cryptic utility markings spray-painted onto streets and sidewalks. Like graffiti tags or hobo codes, this language of scribbled text, dots, lines and arrows may seem indecipherable at first, but lives depend on engineers, city workers and utility companies understanding what they mean.

Utility markings tell excavators working on subsurface projects where to dig and (more importantly) where not to dig. A vocabulary of symbols (with its associated grammar of colors) helps diggers steer clear of dangerous power, sewer and water lines as well as other pipes and cables.

Like any language, utility codes have evolved what one could call regional “accents” of a sort — linguistic conventions that vary from one state or country to the next. Standardization, though, is important in helping keep people safe, which is why there are often local or national rules governing what different colors and symbols represent.

Long before cities came around to the idea of utility markings, train-hopping nomads were working out similarly symbol-based systems of communication. As these travelers roamed America looking for work, particularly during the Great Depression, they learned to leave messages for one another — so-called “hobo codes.” These relatively simple symbols could help fellow travelers find good places to camp and kind people who might give them meals, for instance.

At the time, being nomadic was a mixed bag — some travelers were known as bums or tramps, disparaged for drinking or idling rather than working. The term hobo, though, was more specifically applied to those actively seeking work and willing to take on jobs others didn’t want to do — hobos were met with various degrees of caution and generosity. Many were illiterate, however, so coded symbols with intuitive meanings helped them convey messages through etched or chalked markings. The relatively discreet size and abstract shapes made these marks easy for people not in the know to overlook.

Some symbols represented fairly specific suggestions about how to behave and what to avoid. A cross, for instance, could indicate that talking about religion might help a person get free food from a particular resident. Other markings might caution hobos about heightened crackdowns on vagrants and beggars by local police. While train-jumping culture has changed, some modern travelers have attempted to digitize the idea of hobo symbols through QR codes.

Mural and graffiti art sit somewhere between officially sanctioned and illicit urban communication, depending on the location and surface being tagged. These interventions, too, have evolved a lot over the years. Definitions and genres have sprung up along the way, helpful for tracking and analyzing but also understanding different works — there are pieces, tags, stickers (or: slaps), throw-ups, stencils, heavens, blockbusters, wildstyles and more.

A piece, for instance (short for “masterpiece”) and is usually a complex and multicolored affair difficult to do illegally given the time they take to make. A blockbuster can go either way, often made using rollers and designed to cover up a surface — sometimes one that has already been tagged. A heaven, however, is generally illegal, defined by the difficulty of putting a work up high on something like the back (or front) of a highway sign or the surface of a billboard advertisement — not generally places where one can get official approval to paint.

Some typologies are pretty self-explanatory, like bubble letters or fat caps, the latter of which are usually done with wide spray tips, making them both easy to deploy and easy to read (in turn rendering them useful for get-in-and-out-quickly situations). Shadow letters can also take a bit more work, but help a tag pop off a surface, giving it a somewhat more weighty and three-dimensional appearance. Indirectly, the forms and shapes of letters and symbols tell the observer something about the artist’s intent and constraints. Graffiti can even be broken down into characters, alphabets and fonts, which an informed onlooker can use to better understand a given work.

Some artists and art fans have gone to great lengths to classify different types of graffiti, but such a task is destined to be forever incomplete — graffiti is personal and location-specific, not based on any shared font or type. But some, like artist Evan Roth, try anyway to collect, identify and compare examples of letters, creating order out of the seeming chaos of conflicting tags. He also took his project full circle by pasting up alphabets along the city blocks in which they were originally found, encouraging people to look at tags in a new light, offering temporary glimpses into the linguistic ties that bind them loosely together. With any street communication, legal or illegal, there will always be some give and take between fluid creativity and efforts to categorize, standardize and simply understand.

From Seattle to New York City, Minneapolis to Dallas, boxy apartment and condo buildings sporting bland facades, metallic or colored cladding and a generally flat aesthetic seem to dominate new urban developments these days. Surprisingly similar in style from one place to the next, they have been dubbed works of “developer chic” or “fast-casual architecture” and branded blandmarks or LoMo (Low Modern), generally by those critical of their appearance. Some of their look is a byproduct of “value engineering,” a stripping away of decorative flourishes for the sake of saving a few dollars (the bane of many artistic architects) but there is more to the story.

As with virtually any architecture, costs do naturally play a role as well in shaping these structures — ornate brickwork may look beautiful, but even as a decorative facade layer the material adds loads of weight and a lot of expense to a cheaper wood-framed building.  As for the stylistic convergence more broadly, much of this traces to economic and other factors that are essentially the same across cities in America and otherwise: high demand for affordable housing that has to meet a similar set of safety and other code requirements.

In many cities, housing is in short supply and a lot of area is zoned for single-family residential, forcing developers to fit as much housing as they can into whatever plots are left available. Where they do get built, these structures face restrictions often derived from international building codes, calling for formulaic approaches (for instance: a concrete base floor with five wooden floors on top) resulting in a roughly similar size and shape. Facades with portions that are recessed or pushed out are common features, too, again usually the product of local ordinances and design review boards that demand physical variety from facades.

To some critics, these cookie-cutter creations represent an aesthetic crisis. To others, they seem like harbingers of gentrification. As any urbanist knows, though, a lack of affordable housing is a serious and pervasive problem neither caused nor solved by architects as such. Architecture critic Kate Wagner looks at the situation pragmatically, arguing that “affordable mid and high-rise towers are the most effective way to house the greatest number of people on the smallest parcel of land, something that’s desperately needed in places like San Francisco, where the value of land is so high.”

For those who would point to the much-discussed failures of 20th-century mass-housing attempts, she writes: “Modernist public housing was not the failure of architecture it was the failure of people—through racial prejudices, misguided and poorly thought out policies, ugly politics, and economic greed, people caused the public housing of the past to fail.” Additionally, a lot of lessons learned from that era are incorporated into even the most boring of boxy apartments, including mixed-use programs that activate areas and bring in more than just residents.

More broadly, there is a case to be made that what was once more of an art has become something of a science, whatever one’s opinion of the effects. Architects have always been in the business of balancing aesthetics and pragmatics, form and function, but increasingly their work is constrained by outside forces, including but not limited to client budgets, safety considerations and municipal rules.

Over the long term, the sometimes-shoddy construction materials and methods of this currently trending typology may be the seeds of its undoing. It’s possible these will be looked back on as a mistake. Maybe, though, the same thing will happen here that has with other approaches and styles over architectural history: people will come to appreciate the beauty and functionality in what currently seems mundane if not abhorrent. In the meantime, architects can only do so much — it’s up to cities and their citizens to accept reality or rethink entrenched paradigms and consider the merits of changing zoning limitations, restrictive codes and perhaps also the benchmarks by which we judge architecture to be good or bad.