NR 422 Lab 5: NLCD, Classification and Attributes
For this lab, you will be compiling a short report on land cover in your area and some other
general information about your area. To do this, you will learn a how to take full advantage of
the data you have gathered for your area in addition to downloading some additional land cover
data.
Goals:
 Download NLCD data
 Interpret NLCD data
 Classify and Reclassify Rasters
 Use field calculator, calculate geometry and statistic tools in attribute tables
 Make selections on attributes
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1. Downloading National Land Cover Data (NLCD) from National Map
The USGS National Land Cover Dataset was derived from Landsat Thematic Mapper
satellite data from the past couple decades. If you go to http://landcover.usgs.gov/classes.php
you can find out more about the land cover definitions as well as other useful links. The
following explains how to download NLCD from National Map.
a. Go to http://nationalmap.gov/
b. Click on the National Map Viewers
c. Scroll down until you see the Download National Map Imagery and Elevation Data
d. Choose to view data for North America or Internationally. Choose the view that
pertains to your project.
e. In your window you should see a full extent of North America with Tools available to
you on the left and downloadable layers on the right.
f. Using the zoom tools
, navigate to an area of your choosing that you wish to
obtain elevation data for. At any time, you can zoom back to the full North America
extent
.
g. Zoom into your area of interest. This data is at 30m resolution so you should be able to
download one dataset for your area unlike the DOQQs
h. On the right hand side, there is a navigation bar with Display and Download tabs at the
top. Notice that one of the options is Land Cover.
i. Click the Download tab and then the Land Cover drop down. Notice all the options for
your area
j. Check the box next to NLCS 2001 Land Cover
k. Once you’ve honed in on your area, select the download extent box.
and choose
your area of interest.
l. A Request Summary Page should have popped up detailing what you are downloading.
There may be more than one thing to download if you picked a large area.
m. Click Download.
n. Two more pop-ups will appear. The first tells you that USGS is extracting your request.
The second will tell you that the extraction has been completed and will ask you to save
the zip file (.zip) that it has provided or ask you to click here which will allow to save
the zip file.
o. Unzip your elevation file and save it to your workspace.
p. Repeat this for the other Land Cover datasets if necessary
Remember to Project your downloaded data before using it with your other data!
2. Interpreting NLCD
In this next section, you will learn more about how to take advantage NLCD data.
2.1 Making sense of the colors (Classifying)
a. Open ArcMap.
b. Load your downloaded (and correctly projected) NLCD raster.
c. Right click layerPropertiesSymbology
d. In the Show: window, select Unique Values (What did this just do?)
e. We can see the colors of the different land cover types and a numeric value, but what do
these values mean? Great question lets find the answer. A simple Google search for 2001
NLCD class definitions is all you would need to find this document:
http://www.epa.gov/mrlc/definitions.html
Notice the website is not USGS but if there is any doubt that these values are not the true
values you could cross reference them with other documents or do some more
investigation and find this page http://www.mrlc.gov/nlcd_definitions.php.
f. Depending on which NLCD you downloaded use the definitions to fill in the Label
column in the symbology tab.
g. Take a second to look at the final column, Count. What does this mean? How might this
be useful?
h. Click OK.
2.2 Isolating the information you want (Reclassifying)
There is a lot of good information in the Land Cover raster, but perhaps we are only interested in
a couple values. Here is how you would make a new layer only containing those values
a. To make things easier on us, we will set the spatial analyst options to automatically clip
to out area of interest.
b. Go to Spatial Analyst dropdownOptions
c. In the General tab, set your working directory to where you want to save or load any
files
d. For your analysis mask, select the boundary layer for your study area
e. In the Extent tab, set the Analysis extent to the boundary layer also
f. Leave the Cell Size default value of Maximum of inputs
g. Click OK.
Now that the options are set, we now want to reclassify our NLCD raster to only include the
cover types we are interested in.
h. Go to Spatial Analyst drop downReclassify
i. The NLCD will be the input raster
j. Notice the two columns; old values and New values. We want the cover types that we
aren’t interested in to be No data. To do this, type NoData (one word) in New values
column for all the cover types you are not interested in. Keep the old values the exact
same value in the New value column. An example is below.
k. Save the raster and name it something useful.
l. Click OK.
You should now have a new raster that only shows the cover types you were interested in.
3. Attributes
Attributes are essentially a tabular file that contains columns and rows of information associated
will a class of geometric features. They are important components of spatial analysis. In this next
section, you will learn how to take full advantage of the attributes of your vector data and how to
add more information.
Often we many be interested in the area (lakes, study area) or how the length of a feature class
(roads, streams, trails) we may have in a study area. Fortunately, there are tools provided by
ArcMap that allow us to calculate these values. We can do this by using calculate geometry
3.1 Calculate geometry
a. Open the attribute table for a polyline or polygon layer.
a. Right click layerOpen Attribute Table
b. Add a new field to the attribute table for the geometry of interest (road length, area, etc)
a. OptionsAdd Field
c. Name the field something that makes sense. Be mindful that you are limited on character
length and some names are reserved and cannot be used.
d. For the type, choose float for geometry calculations (this will allow you to have decimal
values and plenty of digits for accuracy).
e. Now that you have a new field, right click the top of the field. Notice all the options
available to you for the field. Select Calculate Geometry.
f. A new window should appear. Depending on your feature class you will see a value in
the property window that you can calculate (length, area, perimeter, centriod values).
g. Choose the property you are interested in and the units appropriate for the feature you are
calculating geometry for.
h. Click OK.
i. Now each feature in your layer should have a calculated geometry associated with it. Take
a minute to investigate what exactly is one feature in your layer. How helpful is this
information?
3.2 Select by attributes
Sometimes you may want to select from your layer features that have a certain attribute value
associated with them. To do this you would use Select by attribute.
a. In the attribute table of your layer you can select attributes by going to:
OptionsSelect by Attributes
b. A window will pop-up. From here you can do all sorts of different queries. When you click
on an attribute name you can get the values associated with the attribute by clicking the Get
Unique Values button. This can be useful in avoiding spelling or value mistakes. Lets say,
for example, you wanted to select roads that are longer that 2km. Your window may look
something like this:
c. when you click Apply, all the features that meet your selection criteria will be selected.
You can them make a new layer that only consists of these selected features by going to:
Right click layerSelectionCreate Layer From Selected Features
NOTE: The data in this new layer have not been saved. To save these data you have to Right
click on the new layerDataExport Data. This will prompt you to save the data for this
layer.
3.3 Statistics
Another tool available in the attributes table is Statistics. This allows you to find the
statistics for a particular field of interest
a. In the attribute table Right click the top of a field of interest ant select
Statistics.
b. A window will appear with a variety of statistics that you can used to describe
your data
4. Raster data
We have explored some of the ways to get more information out of vector data, now we will do
the same for raster data.
a. Load a raster layer into ArcMap
b. Right click the layer and choose Properties
c. Select the Source tab
d. In this table you can find almost all the critical information about the raster layer. Using
this table try to find out the answers to these questions:
a. What is the area of one cell?
b. What type of data does this rater have (integers, signed integers, etc)
c. How is a cell that doesn’t have any information coded?
d. What is the maximum value? Minimum? Mean?
e. What is the datum and projection?
f. What is the linear unit (this may help with the first question)
Some more cartography tips
How to export your map layout
Sometimes the ArcMap layout doesn’t have the flexibility you need to do some layout
modifications. You would have more flexibility if you were to have the layout in a drawing
package such as PowerPoint or Photoshop. Luckily there is a way to export your map.
a. There are some things you have to do in Arc:
1.) Add spatial data (this should be obvious)
2.) Scale bar (This can’t be done accurately in any other package)
3.) Legend (This isn’t a must but Arc does a fairly good job and it would take
quite a bit of time to put one together yourself.)
b. Once you have what you want displayed properly in the data frame you can select
FileExport Map… You can then save it as a .jpg.
c. After you have saved it as a .jpg, you can bring it into any drawing package. Then you
can use Arc to create the scale bar and copy and past the scale bar into the drawing package and
maneuver it however you like. Then you can do the same for the legend.
d. From there the sky is the limit. You could create you own north arrow and put it in.
You could insert your own text; add shapes, pictures, and charts to the map. You could
experiment with the picture contrast and brightness to really make your map stand out.
FINAL TURN IN:
A professional report describing your area that includes: A table of the NLCD land cover types
and the area each covers (*make sure to reference the table in the text), 2 key information values
for 3 layers in your study area (ex: miles of roads, density of roads, average elevation, average
slope, area of north facing slopes, etc). This information can be displayed however you wish
(table, text, map, etc). Also, include a map of a specific area within your study area highlighting
some of the key information and/or land cover types referring to the map in the text. Try to do it
all with less than a page of text.
*Some additional all notes:
Tables have heading and figures have captions. Refer to tables and figures in your text
(ex: The study area has 3000ac of bare ground (table2) which is generally concentrated in
elevations>3000m (figure 3)).