good morning youtube so in the previous video i showed you how i was using these historical
usgs topo maps to look at changes over time so these old maps are interesting and that
they show some details like this map shows these two structures here it doesn't show
anything about the road or roads that got to these structures so anyway about a month ago i caught
this video by a fellow named peter zelinko he used this usgs national map viewer to visualize some of
the geology and topography around some of the ice age flood areas specifically this was up in
central washington state and he did a really good job showing how to use this tool and i
had never seen this before and down here he gave a little bit of a description for that
a link to the page he was using and then a little hint here to use this elevation tinted hill shape
so that got me curious so i went and looked up that map so yeah this is the usgs national
map viewer page so just to give you a little bit of an overview here up here on the menu bar
you have a choice of a dozen different base map so if you want just imagery you can use that i'm just
using the usgs national map here you can bring in lots and lots of external data that you can lay
over the base map there's 10 000 different items you can bring in road density there's elevation
you've got landsat imagery there's over 300 screens full of data you can bring in
but the built-in layers here are what's really powerful and this is what was shown in that video
there's also an imagery layer so you could have the base map with imagery over it or you can have
the imagery base map and put something else over it so lots of options there but there's this whole
group here called 3d ep and that's what's called this 3d elevation program it's run by usgs and
they're collecting high resolution 3d or elevation data using lidar over the whole country and that's
ongoing now this chart here shows where they're at in the u.s so all the dark green
is lidar data the light green is stuff that's in progress or planned and then i think the
white areas haven't been scanned yet so you can zoom in on the pacific northwest
and so that's roughly the view that peter was showing here and you can really see the topography
and the low areas in green and then the higher areas this 3d tinted hill shade is really neat
feature so i thought i would take a look at that layer in the area i've been exploring and just see
if i can see anything different so let's turn that off so you've got san jose sunnyvale mountain view
here's palo alto up here and then this is the stevens creek reservoir and then this is where the
san andreas fault runs up through here so there's a couple things i notice with these layers and the
map is that not all of them support all the zoom levels like here on the map i can zoom in there
and then it disappears i've zoomed in too far for this map so you do have to be aware that there are
limits yeah so before i turn on this hill shade here this reminds me of back in the day you used
to see these ads in the back of comic books for this x-ray vision or they call them x-ray specs
and you could send in one dollar and get these x-ray specs that you could see all sorts of
things see-through skin and whatever you know they were kind of a scam but this is real
you turn that on and now you can see clearly that this is a man-made dam you can see how it's just
a straight line across there here's the outflow or overflow channel for that dam so actually in this
area i find that the elevation tint isn't terribly useful because everything's like two different
elevations so if you get rid of the elevation tin the hill shade feature is a lot more visible
and i think what they do with the hill shade is they're basically projecting
light and then using the 3d topography to cast shadows so i think they're coming over here i
don't know where the light source maybe it's upper left coming down here so you can see you've got
dark shadows over here and then this side of the creek is really light so i think they're bringing
light in from the side you might say well why not just use the aerial imagery isn't that good enough
well here's the aerial imagery you can see the road and you can see these open areas where they
replanted after they did the construction here but you can't see anything you can't see the
pond you can't see the creek it's there but you can't see it but if you turn on the hill shade
suddenly all the trees disappear and you can see right through to the ground level so that's what's
really powerful with this hill shade a couple of trips i made one is i came across the bridge
and then i hiked up here into the pond area and then on the other trip i came up here
and hiked down this area and then across and then you can see there's a really faint trace up there
and i think that's the old road i hiked up and i think they just built the overflow channel down
the old road because it was a convenient way to get up there from this map and from the ground
the overflow used to run all the way down here and then into the creek and then it probably
silted in right here and then started overflowing farther upstream and came out here and down into
the creek and then this plugged up and then it started cutting a new channel farther up
and that's what i saw when i hiked out there was this looked really freshly eroded
where this had started to grow over already
pretty much the map confirms what i saw on the ground but you can see here that there used to be
a road continuing all the way down here looking at this i saw that there was probably a road coming
up here too and then there's even a third road that comes up this hillside and hooks in over here
so there's a bridge right here and that bridge was probably around back then and it lets you
go over this way and uh so yeah this area here actually had three different roads feeding it
and then the other thing i was looking at on the 1961 map it showed a dwelling or structure up here
and then the 1897 map showed a road that came up this canyon and actually went up here
so you can actually see traces of that road up here
and then this road here is very visible so this is the hill shade view which is just a single light
source and then they have this multi-directional hill shade which uses multiple light sources you
have to switch back and forth between these because some things like this road up here is
really clear in the multi-directional it's visible in the regular hill shade but it kind of fades out
now this road shows up better in the hill shade and it fades out in the multi-directional
but then you can see over here like the uh overflow channel is really clear you can see
the road is much wider in the multi-directional here it's just a faint line so you have to play
around with these three here there's the elevation tinted shows certain things the multi-directional
shows other details and then the regular the plain hill shade shows other details you can't
just pick one you have to try all of them and see which works best for your particular area
but yeah we'll take a look at this area in the next video try exploring up here
see if this old road exists and what's up here just as a future exploration if i get a chance and
right up here looks like there was an old road headed up that direction and the
multi-directional hill shade even shows it up even clearer and you can see that going way up here
and i think it goes clear up here but then there was also signs of a
trail or something up this side too so there's a lot of detail you can see up here so there is
one major limitation of this hillshade feature is that this is a web page i zoom out
it takes a while for the web application to download that information and this isn't just
a map this is a bunch of tiles that are computed the real limitation of this is you need a live
internet connection to be able to view this data so that's one limitation and up here there's no
cell service the other limitation is even if you could get a cell signal up here there's no gps
coordinate feeding into this so your gps receiver can't tell you where you are on this map just a
static map it doesn't show you your live location so supposedly gaia gps is working on some sort of
hill shade solution they do have this terrain hd again it's got limit you can only zoom in so far
like there i get a full map but if i zoom in a little bit i only get this little tile
i don't get any data down here so yeah you've also got a similar thing in google maps so you do
get this terrain shading option which is similar to what gaia terrain hd is and you can get some
faint hints like there might be a dam there it's just such low resolution and as you zoom in it
basically disappears if you zoom out far enough it looks pretty good and then likewise this terrain
view does not work if you don't have a data connection you can go into google maps and save
a map set but that only shows you the regular map so you can see this map with no data connection
but you can't see the terrain map with no data connection i'm still trying to figure out how to
use this data out in the field it is a really powerful tool and i'm hoping
that at some point gaia gps includes some version of this map or this layer
in their application for offline use this map is really powerful so i'll be showing you more of
this in the future but i just wanted to introduce this and if you haven't seen it it's really neat
for looking at this kind of information looking for old roads or old building sites
things like that so yeah there are some limits but yeah in the next video we'll
take a look down here and see if this actually is a road and see if there's something up here
and see what we can find so stay tuned for that video and as always thanks for watching