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.

In a world of pristine and perfect model architecture, this replica of a locksmith in Taiwan boasts dirt, grime, graffiti and rickety structural details.

Crafted by Joshua Smith (images by Ben Neal), this 1:18 scale micro-structure lights up at night and takes on a particularly compelling realism in the relative dark.

Ballpoint pen plastic is worked in to flickering lighting fixtures while tagged walls and a rusty motorbike give it a sense of character and scale.

Smith’s newest miniature will be on display from November 10, 2017, at the Arcade Art Gallery in Taiwan as part of the group exhibition When the Sun Goes Down.

Based in South Australia, Smith previously worked for sixteen years as a stencil artist, and has now shifted his focus to model-making, with an emphasis on urban realism. Be sure to check out more of his work here as well.

Tapping into geo-tagging data and the collective wisdom of photographers, you can use this interactive tool to follow in the footsteps of those who have mapped out the most beautiful routes through cities. Click to pan and zoom through London below:

Eric Fisher of Mapbox has spent years compiling data from Flickr users, turning their sequential geo-located uploads into paths through urban environments including San Francisco, Beijing, Istanbul and Tokyo.

The result is the Geotaggers’ World Atlas, a data-driven compendium of paths to take through cities. It is more than just a connection of dots — Fisher’s interactive guides specifically highlight trajectories from one image to the next.

“It signifies that people went there in the first place,” he says, and “saw something worth taking a picture of, and put the extra effort into posting it online for others to appreciate. And a sequence of photos along a route is even more significant, because it indicates that someone sustained their interest over distance and time rather than taking one picture and turning back.”

The results are predictable in some cases, tracing lines between major landmarks, but often show side routes off of beaten tourist paths where keen photographers have found fascinating architecture and landscapes worth documenting along their way.

3D graffiti artist Milane Ramsi has combined two challenging types of urban art into a single installation, making a concrete pillar appear to vanish while producing three-dimensional lettering.

The installation wraps a concrete support post for a highway overpass in Karlovy Vary, a city in the Czech Republic. The work spells the artist’s name in reverse, appearing to pierce the pillar thanks to a combination of colors overlaid on a simulated background. The purple gives a general shape to the work while the yellow adds apparent depth and dimension.

His other works range from tags to 3D-looking works that appear to pop off the wall, but this particular piece combines elements that span graffiti types and styles.

In invisibility aspect is reminiscent of another clever work of roadside art, a wrapped tree designed to look like it has been cut across the middle, leaving the top half portion of the trunk and branches to seemingly float on air. And below: Tree Line by photographer Zander Olsen.

Calculated correctors, this team of vigilante street art fixers patrols for grammatical mistakes then regroups to decide on edits before hitting the streets of Quito, Ecuador, to deploy them.

Known as Acción Ortográfica Quito, the group consists of a trio who share a strange set of common interests including street art copy editing. Like rogue professors, they use red to highlight their changes or suggestions, but their good intentions do not render their actions legal, hence their strictly maintained anonymity.

“There’s a big difference in saying: ‘No quiero verte’ (I don’t want to see you) and ‘No, quiero verte’ (No, I want to see you),” notes one of the members in an interview with COLORS, “Many times, someone does not realize how a comma or an oversight can completely change the meaning of a sentence. It can change your life.”

The task can be daunting – their first fix had thirteen errors in two lines of text. Whether serious or silly, they suggest “it’s a public service and a moral obligation. We’re against spelling vandalism and we won’t break nor give up until we see a society free of spelling mistakes.”

Above, the phrase: “If in your kisses I met the essence of life, then not kissing you would be the worst sin I could commit,” for which these graffiti activists turned the verb into conditional, added and deleted commas, turned ellipsis into full stop and capital letter into lower case.

The group is also broadening its scope and mandate over time; they are aiming to add a hotline where people can phone in mistakes they spot and have begun correcting grammar on Twitter posts as well. When time permits, they also leave their name stenciled at the scene in red, like a grader signing their work for students.

Meanwhile, a similarly unconventional yet equally geeky German street artist is out to fix tags, turning them into tag clouds – it would seem this group is not alone in its quest to clean up yet preserve the essential meaning of everyday graffiti.