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En provenance du cours de University of California, Davis

Imagery, Automation, and Applications

314 notes

University of California, Davis

Imagery, Automation, and Applications

314 notes

Cours 4 sur 5 dans Specialization Geographic Information Systems (GIS)

Welcome to the last course of the specialization (unless your continuing on to the capstone project, of course!). Using the knowledge you’ve learned about ArcGIS, complete technical tasks such raster calculations and suitability analysis. In this class you will become comfortable with spatial analysis and applications within GIS during four week-long modules: Week 1: You'll learn all about remotely sensed and satellite imagery, and be introduced to the electromagnetic spectrum. At the end of this week, you'll be able to find and download satellite imagery online and use it for two common types of analysis: NDVI and trained classification. Week 2: You'll learn how to use ModelBuilder to create large processing workflows that use parameters, preconditions, variables, and a new set of tools. We'll also explore a few topics that we don't really have time to discuss in detail, but might whet your appetite for future learning in other avenues: geocoding, time-enabled data, spatial statistics, and ArcGIS Pro. Week 3: In week three, we'll make and use digital elevation models using some new, specific tools such as the cut fill tool, hillshades, viewsheds and more. We'll also go through a few common algorithms including a very important one: the suitability analysis. Week 4: We'll begin the final week by talking about a few spatial analyst tools we haven't yet touched on in the specialization: Region Group to make our own zones, Focal Statistics to smooth a hillshade, Reclassify to change values, and Point Density to create a density surface. Finally, we'll wrap up by talking about a few more things that you might want to explore more as you start working on learning about GIS topics on your own. Take Geospatial and Environmental Analysis as a standalone course or as part of the Geographic Information Systems (GIS) Specialization. You should have equivalent experience to completing the first, second, and third courses in this specialization, "Fundamentals of GIS," "GIS Data Formats, Design, and Quality", and "Geospatial and Environmental Analysis," respectively, before taking this course. By completing the fourth class you will gain the skills needed to succeed in the Specialization capstone.

À partir de la leçon

Digital Elevation Models and Common Algorithms

In this module, we'll be looking at DEMs and workflows. In the first half, we'll make and use a handful of products derived from digital elevation models, including contour lines, hillshades, viewsheds, and the cut fill tool. In the second half of the module, we'll go through a few common algorithms, starting with one of the most important ones to know: the suitability analysis. Then, we'll learn about the hydrologic processing you did in the tutorial assignment for the previous module and go through it step by step together.

Module 3 Overview0:36

Rencontrer les enseignants

Nick Santos
Geospatial Applications Researcher
Center for Watershed Sciences

[MUSIC]

Hello everyone and welcome back.

In this lecture, I'm going to show you how to use and label contours in ArcGIS.

For those of you who don't know what the contour is well, let's go take a look.

So we're going to use the same map document that we used last time with

the Navarra river digital elevation model and in the same toolset,

the Surface toolset in Spatial Analyst, I'm going to run the Contour tool.

So I'll double-click it, provide this raster as the Input raster,

and I'm going to call it navarro_contours_ 80 because

I'm going to space them by 80 meters and

we'll leave the base contour as zero and the z factor as one.

So I'll click OK and I'm going to go back through that a little more slowly in

just a moment, but we want to have some contours to look at right now, so

that we can understand really what they are.

So, if you've never seen a contour before, or

maybe you just haven't heard of it as a contour, it's a topographic map.

Where if we don't have a digital elevation model

Instead we can use these contours to see what the elevation in an area is.

And each line stays the same elevation.

So if you follow a line you stay on the same elevation.

And in between two lines, you're somewhere in between those lines' elevation.

So in practice, the lines need to be labeled with the contour spacing.

And here we get kind of odd numbering,

but I suspect that that's actually because of what the labeling is using.

I bet it's using the feature ID or

something rather than the contour interval.

So yeah, it's using the ID, so let's label it with contour.

And if I click OK, I can now see what makes more sense, so

in here I have a line where the whole line is at a 160 meters of elevation.

And then the next line up is at 240, and if we turn on our digital elevation model,

we can see that, yeah, that's going up slope.

Then this line's at 320 meters and the next line should be at 400 meters and

then 480 and then 560 here all the way up this peak.

This little peak and then 560 here and then a small peak at 640 as well.

So, we get this lines of consistence elevation and in between them,

somewhere between those contour lines, somewhere between those elevations.

So for those of you who knew a contour was or topographic map, and

how to use it to read elevation.

Well you can make them in ArcGIS with a digital elevation model.

And we can choose a few different parameters related to it.

We don't have to do 80 feet of spacing, we can do smaller spacing as

long as our digital elevation model actually has that resolution.

So, maybe we want to try 50 meter contours or even 40 meter contours.

So, we could do that.

And we can also set the base value.

So, maybe we don't want to start at sea level or

something like that or if our raster doesn't start at zero.

So, maybe our raster doesn't go all the way down to zero.

We might want to start at the level that the raster starts at.

And the last thing here is, it's possible that the units of our Z units in a raster,

our vertical units in a raster aren't the same as the horizontal units in a raster.

So, maybe for whatever reason I have a raster whether projection has the pixels

and meters x and y but that the z values are measured in feet which does happen.

It's possible I would need to a z factor to convert between feet and

meters in a case like that since it's going to interpret

the values in a raster the same way as the projection values.

So here we might specify a multiplier of point three three or

something like that to approximately get out a meter

if our units were in feet in our raster z units or something.

In this case they are not, so I am going to set it to one.

Since it's a multiplier, it's going to multiply the values by one and

give us the values we already have.

So I can naturally make 40 meter contours and then I get

a higher resolution topographic map that in some cases is a little more cluttered.

So sometimes we think more resolution's better but

if you zoom out to the whole area you might actually want that 80 meter or

even a less precise set of contours on your map.

Okay so once we know how to create them what about effectively labeling them so

let's work with the 80 meter contours for now.

Now these labels aren't all that effective and let's turn off the raster behind

it for now and let's make these more of a color that they would be on a hill shade.

Make them kind of a brownish or something.

And let's get into labeling a bit.

So I'm going to turn on the labeling tool bar.

And we're going to use the Maplex labeling engine which

is standard with ArcGIS now but you haven't used it yet unless you did

an extra practice assignment in the third course of specialization.

That had you working the Maplex a little bit and

it's honestly if you're going to do much with labeling at all I highly recommend

using it instead because it has far more features and you can fit a lot

more data in your map without making it feel cluttered with Maplex.

So, with the labeling toolbar, I can select Use Maplex Label Engine.

And immediately, it starts putting more labels on my map,

which isn't necessarily a good thing right off the bat.

But if I go to Label Manager, I now get

all kinds of new options I wouldn't have had before in terms of labeling.

So let's select the default label class for the Navarro contours.

And first thing, I want to change the placement.

Right now it's kind of near the line, but that can be hard to tell what's going

on in situations where, like down here where there are contours close together,

so in steeper slopes or something like that where the contours get really close.

So let's instead of making it straight near the line let's change the position.

And a common thing for contours is centered and curved with the line.

So I'm going to click OK.

And click apply.

And immediately my contours or

my labels become in line with my contours here, which is really handy.

But now they're hard to read.

If this was labeled a little differently it be hard to tell which of these was 480

versus 400.

So let's open our Label Manager back up and

let's change the symbol on our text so, that we can read a little bit better.

I'm going to make it kind of a dark brown itself but

then in background of it, I'm going to give it kind of a halo,

so that we can read it no matter where we're looking at.

And we've done this before with the rivers and

I'll make this kind of a light background, light gray,

click OK and let's Apply it to see.

Okay, it's not perfect but that'll work.

Maybe I'll just make it slightly thinner first.

So let's make this a one-point halo I'll click OK and Apply, and there,

still not perfect but it's going to be great for now.

That looks nice to me, one thing I might also want is to

have these contour intervals repeat so that I don't have to

trace the 320 all the way along the line to figure out it's 320.

I might want the numbers repeating, so open my labeling manager back up,

and in properties, under label density, I can go to repeat label.

And I an go to options, and

I can tell it how far away in meters it should add another label.

So let's maybe say every half a kilometer or so, so

let's say every 500 map units because this map is in meters, as we can see down here.

I'll click OK, so every half a kilometer it's going to repeat the label.

And, let's see.

That looks like quite a lot.

So maybe it should be one kilometer instead.

I'll go to Options.

And change it to 1,000 map units.

And just looking around here you could see all kinds of options that we're

not going to go through.

I highly recommend doing that extra practice in the previous course if you

are interested in labeling.

And then click OK and click Apply.

And that's better.

These are repeated but not super close.

And then one last thing, if we actually go back into the labeling or

to the label manager Is to switch to contour labeling in particular.

So we've been doing this stuff manually to make it look like this.

But if we go to position, oops.

If we go to Properties, and under placement options here,

I can select Contour Placement.

I then get some new options in here specific to contour labeling.

And I can tell it whether or not the labels should be aligned so

that you can always read them from the page, or whether they should be aligned so

that they always face uphill.

And I'm going to leave them at page alignment,

and then I can select laddering options here.

If I go to no laddering, it does what it's been doing before,

before we select contour labeling and contour positioning.

But contours, by default, will do placing labels in ladders,

so that it will try to give you labels aligned

in such a way that you can just go straight up the hill with them.

So I'll click that, I'll click OK, and I'll click OK, and

what we get Is where possible it's trying to put these labels in a line.

It misses in some spots like this 240 seems like it should be in here and

these should be kind of all along here but

it does an okay job of it at least with these contours.

One last thing I'll mention just because I like it, is that if we have a hill shade

saved, just a standard hill shade, I'll just make it quick so that we can show it.

One thing I tend to like to do with contours is use them as a sort of light

bit of tinting, instead of having the digital elevation model show color.

What I might do is what we did before, I'll make this show the DM below it.

And then I'll make the contours have

a color based upon their elevation themselves.

So, if we've got a symbology and we've got quantities,

we can select kind of an elevation tinting pattern in here.

We'll use that one.

And I'll use the contour value and make it have maybe ten classes instead.

And I can apply, and then you can see the elevation based upon the contours,

which aren't quite as intrusive in the color as everything else until you zoom

out a bunch more.

I tend to not like this particular elevational banding, so

I'll usually do something a little more subtle,

like I might do like a white to pink or something like that.

But, that way, as it gets more red, you know that you're higher up but

it's not quite as heavy as

the hips metric tinting pattern of doing the full digital elevation model.

So I'll usually use this when I'm working with my data as I navigate around this

lets me at a glance see what the elevation is.

Without having massive amount of color that obscures the rest of my data

once I zoomed in but I won't usually published a map like this.

Okay, that's it for this lecture.

In this lecture we learned about how to use contours, how to create them and

then also how to label them for use on your maps.

Next up, we'll continue learning a bit about using digital elevation models, but

we'll start to dig more into analysis rather than

viewing data based on our digital elevation models.

See you there.

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