- Hi, I'm Sean Romo, senior staff archaeologist
with the Jamestown Rediscovery Foundation.
And I'm down here at our seawall excavations,
where we're going to talk a little bit about archaeological mapping.
Welcome to another episode of "Dig Deeper."
[music]
[trowel scraping]
So we're down here at the seawall
excavating adjacent to an area we dug 20 years ago.
Now, when you're doing archaeology, mapping is very important,
and making sure the map is accurate is very important,
because we rarely have the full breadth of the site open all at once.
In fact, we typically do small excavation areas like this,
piecemeal, every year or so.
And so we're only getting a snapshot of what's under our feet
and then moving on to adjacent areas once this is already closed up.
Having the map be accurate and very precise
is helpful because we know, then,
if we find a feature here and we find one in the next excavation area,
they're precisely located, so if we're going to make measurements
or try to identify site-wide patterns, we can.
Now, 20 years ago, when this area was being dug,
the person in charge of mapping was Elliott Jordan.
And Elliott, we have to say you did a great job,
because you can see here one of our old excavation nails,
and our new nail is exactly over top of it.
This means that the work that was done 20 years ago
and all the mapping that went into it
and our work today lines up exactly,
so everything we find now is going to be able to be compared
to the older stuff from 20 years ago
without concern that the map is inaccurate, and this is a really big deal for us.
So Elliott, good job.
So when we're mapping in our archaeological finds,
our features or sometimes artifacts we've encountered,
we're usually using our surveying equipment, this total station.
And the way it works is that a laser is shot
from this lens here, and it reflects
off of a mirror on top of our stadia rod.
Now, the stadia rod gets positioned on top
of whatever feature we're trying to record the location of,
and the time it takes for the laser to return to the machine
and the angle at which it returns tells the machine
where that point is on our grid,
and then I can see it on the map on this data collector
that's wirelessly connected to the total station.
Now, we use the same grid that the National Park Service
established way back in 1934
when they first began archaeological work on the island.
And the reason we maintain that same grid is continuity.
We want to be able to easily locate the things they uncovered
and compare them to what we've found,
and using the same grid is the best way to do that.
After we do our mapping in the field, the digital data that's recorded
on the data collector gets imported into our computers,
and from there, we put it into
our geographic information system, or GIS system.
And what that is is essentially a map and a database combined.
So we can see exactly where our archaeological features are on our grid
and encode information about them--
when they were created, when we saw them, and what we think they are.
Now, that's important for looking at the site as a whole.
We can see on our map every burial
that we've encountered in the past 26 years,
or every artifact concentration,
or every post hole that we think is from 1607.
And that allows us to put the pieces back together and figure out
which buildings are where, how the land was used in the 1600s,
and all sorts of other things.
So we don't just use our surveying equipment
to map out the archaeological features.
We've actually also been using it as part of photogrammetry.
So when we're digging in a particular area,
we'll take a series of photos in a 360-degree arc,
and those photos get stitched together into a 3D object.
But a major component of those is knowing where a set of ground control points are.
And if you look at this image here,
you can see small nails with Xs marked on them.
Those are our ground control points.
We use our total station to mark out
where those points show up on our archaeological grid.
Knowing that information allows the computer program
not only to stitch the photos together accurately,
but then to be able to place the resultant image in our GIS system,
having it jump exactly where it's supposed to be on our archaeological map.
And so we don't necessarily need to even map in the features.
We can do this photogrammetry and see where they are
as a photograph in the mapping system.
Now, we've been using the photogrammetry more and more here at Jamestown,
in part because it shows such great detail for the archaeological features.
We get a photorealistic image with only taking a few points,
which is a little bit sharper than our hand-mapping
or digital mapping has been in the past.
In fact, we've gotten our accuracy down to less than a 10th of an inch,
which is pretty darn good.
I hope you've enjoyed this little overview
of our archaeological mapping techniques,
and we really hope to see you in the field.
Come see us in person, and catch us in action.
Thanks for watching "Dig Deeper."
[music]