ASTER is a technology that was used to create digital eleva on models (DEMs) for the en re globe at a 30 me-
tre resolu on, which means each pixel is 30m x 30m and has one eleva on value assigned to it. Global Mapper
is a viewer capable of displaying eleva on datasets and allows users to create contour lines from DEMs. If you
have a site outside Canada for which you need eleva on contours, this is how we recommend obtaining them.
While users can download a free trial version of Global Mapper at h p://www.globalmapper.com/, this version
is not the full version and does have considerable restric ons that do not allow the user to export to any file
type. The Global Mapper found on the GIS Worksta ons in MADGIC on the lower floor of the MacOdrum Li-
brary has full func onality.
www.library.carleton.ca/find/gis
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Crea ng contours using ASTER DEM and Global Mapper
This help guide will show you how to: Find a digital eleva on model (DEM) for your area
on the ASTER GDEM website
Load a DEM into Global Mapper
Find your loca on in Global Mapper
Create contours from the DEM in Global Mapper
Export the contours to .DWG or .SHP formats
1. Find a DEM in ASTER GDEM
a) Go to the ASTER GDEM website and zoom to your general
loca on (e.g.: if your loca on is a small town in southern
France, zoom into southern France) using the -/+ slider.
b) When you are zoomed in, click Start in the top right and
click on the area your loca on is in. A blue le will ap-
pear. If you think your loca on is between les or you’re
not quite sure where it is, select mul ple les using the
cursor.
c) Once you have selected your les, click Next. This will
take you to a screen to confirm your les. Click Next
again.
d) You will be prompted for a username and password. Both
are madgicGIS. On the next page select a purpose and
Agree. On the download page, click Download.
e) Once the file is downloaded, unzip it, then unzip the indi-
vidual le(s). You are now ready to make contours!
Zoom
Selected le
Figure 1: the ASTER GDEM interface
Figure 2: selec ng les in ASTER GDEM
Remember: you can always contact us at the MADGIC reference desk in the library, or at [email protected].
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Global Mapper 2. Loading your DEM into Global Mapper
a) When you first open Global Mapper, it will look like Figure 3 below. Click on the third op on
to Download Free maps/Imagery from Online Sources.
b) In the Select Data Source box, expand WORLDWIDE DATA and scroll down to choose Open‐
StreetMap.org Global Street Maps. Once it is loaded, zoom into the general area of your lo-
ca on (e.g.: southern France) using the zoom tools (seen in Figure 5 at the bo om of this
page).
c) Once you have zoomed to your general area, use the
Open Data Files bu on (Figure 5) to add your DEM. It should
show up as in Figure 4 on the le .
d) Zoom in again so the DEM fills the screen. Then turn it
off by going to the Control Centre bu on (shown in Figure 5 at
bo om of page). The DEM overlay name will start with
<ASTGTM. Uncheck the box and the DEM should disappear.
e) At this point, confirm that your precise loca on (city,
street, etc.) falls within the area your DEM just covered. If not,
start again in Step 1. If you chose well the first me (hooray!), zoom into your precise loca on
with the DEM turned off. In this example, rue Joachim Murat in Cahors, France, is used (seen
in Figure 9 on the next page).
f) Once you have zoomed in to your sa sfac on, turn the DEM back on. It should completely
cover the screen. It will probably be a bit fuzzy because remember, it is only accurate to every
block of 30m x 30m, which is almost 1km2. The contours will look fine but they’re generalized.
g) You are now ready to generate contours, which is in Step 3 on the following page. You’ve
completed the hardest part and are almost done!
Figure 3: the opening window
of Global Mapper
Figure 5: The main tools on the Global Mapper toolbar
DEM le in
southern France
Figure 4: DEM in Global Mapper
Control Centre
Zoom
in/out Measure Pan Iden fy
Show 3D view 3D Eleva on Profile
Open Data Files
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Global Mapper
a) Click File, then Generate Contours… This will open the contours Op ons win-
dow, as shown in Figure 6.
b) First, fill out the Contour Interval you would like. If your area is hilly (like Ca-
hors, France), then a 1-metre interval is not recommended. However, if you
have a flat area, you will probably want to get 1 metre intervals. You can do
this more than once so experiment un l you get your desired result. In this
example, the contour interval is 5 metres. Remember: as the DEM has one
eleva on value for every 30m2, the contours will be es mated/generalized.
c) Next – and this is very important—click on the Contour Bounds tab and select
All Data Visible On Screen. Otherwise, contours will generate for your en re
DEM which will take several moments. Click OK.
d) Your contours will generate and will be visible on screen. Repeat steps B and C
un l you are sa sfied with the results, using the Overlay Control Center to
toggle overlays on and off. Turn off the DEM to see what it looks like (Figure
8).
e) Once you are happy with the contours, click File, then Export Vector Format…
f) Select your desired output format (e.g.: DWG, Shapefile). Click OK. Click OK
again if you get a warning.
g) If expor ng as DWG, make sure to click the Generate Projec on (PRJ) File
checkbox (Figure 9). This will ensure that your DWG contours will show up in
the right loca on on the surface of the earth.
h) Choose your file loca on and filename, then click Save.
i) Pat yourself on the back—you’re done!
3: Genera ng contours from the DEM and expor ng result
Figure 6: the Contour Op ons window
Figure 7: the Contour Bounds tab
Figure 8: the newly created contours in the area around rue
Joachim Murat in Cahors, France.
Figure 9: clip from
the DWG Export
Op ons dialog box,
with Generate Pro-
jec on (PRJ) File
checked.
Remember: you can always contact us at the MADGIC reference desk in the library, or at [email protected].