GIS Archaeology: Following the Clues Left Behind

By Kevin Mayo, Founder, FLIPSIDEGEO

Every GIS department has artifacts....

Old layers. Forgotten web maps. Legacy services nobody wants to delete because nobody is quite sure what depends on them.

Sometimes the challenge isn't finding the data. It's understanding the decisions that created it.

While working on a recent project, I found myself following a trail of clues through old maps, archived files, HTML image maps, and historical GIS data. Somewhere along the way, I was reminded of a photo I knew existed but hadn't seen in years.

After a little archaeology of my own, I eventually tracked it down in a Fall 2008 ArcNews article featuring my longtime friend Todd Remmel and me during a surfing trip to Nicaragua. The photo had nothing to do with the project, but finding it felt oddly appropriate. Nearly two decades later, I was once again piecing together fragments of the past—this time not to recover an old surf photo, but to reconstruct the history behind a GIS dataset.

The experience sparked an idea.

What if we treated legacy GIS systems the same way archaeologists treat historical sites?

Not as mistakes to be corrected, but as collections of clues left behind by the people who built them.

That's what this series is about.

GIS Archaeology: Following the Clues Left Behind.

The Discovery

The project started the way many GIS archaeology projects do: with a collection of artifacts.

There were maps, geodatabases, archived files, web resources, supporting documents, and enough historical information to suggest that everything should make sense.

It didn't.

At first glance, the challenge appeared straightforward. The data existed. The maps existed. The applications existed. Yet the deeper I looked, the more questions emerged.

Which datasets were authoritative?

Why were there multiple versions of the same information?

What was the relationship between the maps, the data, and the documents that accompanied them?

Most importantly, how did all of these pieces fit together?

Like any good archaeological dig, the first step wasn't making assumptions. It was cataloging the evidence.

One clue led to another.

A map referenced a dataset. A dataset referenced a document. A document pointed to an older source. Historical files revealed decisions that made perfect sense at the time but had become increasingly difficult to understand as people moved on, technologies changed, and institutional knowledge faded.

The investigation gradually revealed something important.

The problem wasn't missing data.

The problem was missing context.

The original authors understood how the pieces fit together. Years later, many of those connections existed only as clues scattered across folders, file formats, applications, and systems.

What remained was a trail of breadcrumbs.

The challenge was no longer finding information.

The challenge was reconstructing the story behind it.

That's when the real archaeology began.

Following the Clues

Once the evidence was organized, the investigation shifted from collecting artifacts to understanding how they fit together.

One of the first clues came from a set of HTML ImageMapper files. For anyone who has been around GIS long enough, these were a blast from the past. Before modern web mapping platforms became commonplace, ImageMapper was often used to create interactive maps from static images. Click on an area of the map, and a popup would provide additional information.

What looked like a simple collection of web files turned out to be much more valuable.

Buried within the HTML were polygon coordinates defining clickable map features. Separate popup files contained names, descriptions, comments, and other information associated with those polygons. Individually, the files were interesting. Together, they began to reveal how the original application had worked.

The next challenge was connecting those pieces back to geography.

Historical map images had to be assembled and aligned. Polygon coordinates extracted from the HTML needed to be transformed into GIS features. Popup information had to be matched back to the correct locations. Each step answered one question while creating two new ones.

Slowly, the picture became clearer.

What initially appeared to be disconnected files were actually pieces of a larger system. The imagery provided context. The HTML provided geometry. The popup files provided attribution. None of the components were especially useful on their own, but together they told a coherent story.

The process felt less like GIS analysis and more like forensic reconstruction.

Every recovered clue increased confidence in the next clue. A location found in one source could be verified against another. A name appearing in a popup could be matched to a feature. A map image could be compared against modern GIS data. Over time, assumptions became evidence.

By this point, the technical work had become secondary.

The real challenge was understanding the intent behind the information and preserving that understanding for the people who would inherit the project next.

The goal wasn't simply to recreate data.

It was to recover context.

What We Learned

One of the things I enjoy most about these projects is that they almost always reinforce the same lesson.

The goal isn't to prove anyone wrong.

In fact, the opposite is usually true.

Most of the systems, maps, applications, and datasets we inherit were built by capable people trying to solve real problems with the tools, requirements, and information available at the time. The decisions they made often made perfect sense when they were made.

The challenge is that time has a way of scattering the breadcrumbs.

People change roles. Consultants move on. Technology evolves. Servers are replaced. Applications are upgraded. Documentation gets lost. Institutional knowledge slowly fades into memory.

Eventually, someone is left looking at a map, a service, a locator, or a dataset and asking a simple question:

"Why was it built this way?"

That's where GIS archaeology begins.

The most successful projects aren't the ones where old work is discarded and replaced. They're the ones where enough context is recovered to understand what should be preserved, what should be improved, and what no longer serves a purpose.

The real value isn't in recovering data.

It's in recovering understanding.

Because once the story behind a system is understood, it becomes much easier to leave better clues for the next person who inherits it.

And that's ultimately what good GIS stewardship is all about.

Until Next Time

Every GIS contains artifacts.

Some are obvious. Others remain hidden in old maps, forgotten services, archived files, and decisions that made perfect sense years ago but have long since lost their context.

The challenge isn't simply preserving data.

It's preserving the story behind it.

Fortunately, the clues are usually still there for those willing to look.

This project reinforced the importance of leaving better clues behind for the next generation. Good metadata. Meaningful documentation. Clear workflows. A few extra breadcrumbs that help future GIS professionals understand not only what was built, but why.

It also served as a reminder that some artifacts are personal. While following one trail of clues, I unexpectedly reconnected with my longtime friend Todd Remmel after rediscovering an old ArcNews photo from a surfing trip to Nicaragua nearly two decades ago.

So document your work. Leave good breadcrumbs behind. And every once in a while, reach out to an old friend and see how they're doing.

This won't be the last excavation.

Until next time...

GIS Archaeology: Following the Clues Left Behind.