Exercise Title: Managing Global Coastline, River and Lake
Vectors: Global Self-Consistent, Hierarchical, High-Resolution Geography
Abstract: In this
exercise you'll learn about the GSHHG database, which replaces the older
global coasts, such as the GEBCO shoreline. GSHHG includes large
parts of the older coasts (especially the World Vector Shoreline, also
in GEBCO), and other feature sets, and is
part of the
Generic Mapping Tools (GMT) system of map generation. With
the GEODAS-NG software (also to be installed here), you can quickly plot
any area of the globe, in various scale levels and from a flexible list
of components. The plot contents can be exported in a host of
different formats, including shapes (for use in GIS and other
applications), and a special text file product ("XY0" files) that can be
plotted as shoreline points in GIS or alternately used as relief data
for data gridding with your own depth (or height) datasets.
Preliminary Reading (in
OceanTeacher, unless otherwise indicated):
|1. First, open the GSHHG
website and take the time to read about. In all MDL exercises it will
be replacing the very similar GEBCO coastline.
|2. Scroll down the opening
page and take note of these descriptors of the data. Please note the
levels of resolution and other organizational details.
Because MDL prefers the very
administrative borders and the
marine boundaries, the last section ("BORDERS")
is of lesser interest.
"The geography data come in five
Original (full) data resolution.
High resolution: About
80 % reduction in size and quality.
resolution: Another ~80 % reduction.
Another ~80 % reduction.
Another ~80 % reduction.
Unlike the shoreline polygons at
all resolutions, the lower resolution rivers are not guaranteed to be free
SHORELINES are furthermore organized into 6 hierarchical levels:
L1: boundary between
land and ocean, except Antarctica.
L2: boundary between
lake and land.
L3: boundary between
island-in-lake and lake.
L4: boundary between
pond-in-island and island.
L5: boundary between
Antarctica ice and ocean.
L6: boundary between
Antarctica grounding-line and ocean.
RIVERS are organized into
10 classification levels:
L1: Permanent major
L2: Additional major
L3: Additional rivers.
L4: Minor rivers.
rivers - major.
rivers - additional.
rivers - minor.
L8: Major canals.
L9: Minor canals.
BORDERS are organized into
three levels (read the special note above about these data):
L2: State boundaries
within the Americas.
boundaries." [From the website]
|3. Now go to the NGDC data
download site (link above) and get the rather large zipfile and save it to
the folder DATA > BASEMAP > BORDERS > GSHHG on your computer.
|4. Then unzip the
file in place. Check to make sure you have these folders:
Now you're ready for the software.
|5. Take a few minutes to read about GEODAS-NG
at the link above. Then download the latest Windows Desktop Software
version (and its companion README.TXT file) to a convenient location.
Follow the instructions to install the program (using the defaults to make
it easy). Note that you will have a
cluster of related software programs in GEODAS-NG, as you see here in the
screen capture from Windows Explorer.
We will only be
using the Coastline Extractor, a stand-alone EXE file.
|6. Find the new group of
program icons in your Windows Explorer and run the Coastline Extractor.
|7. The first time it runs, it
never sees the data files it needs, so it gives you this message.
Click on BROWSE to fix it.
|8. Navigate into your folders
and find this folder. then click OK.
NOTE: This is the correct folder selection, i.e.
GSHHS_shp, but in some PCs you must open the subsidiary folders to make
this choice succeed.
|9. Now the plotting window
|10. Select COASTLINES+ to
make sure you are going to use the GSHHS data (the old name for GSHHG).
|11. Click on FILE > PLOT and you'll
get this message. Click ACCEPT if you agree with the conditions.
NOTE: This is a very important issue. Don't even think about
using these data to make a "chart" for anyone with a boat.
|12. Now, in the spaces
provided, enter the coordinates of your area of interest. Note where
the negative values should be. If you get a crazy map, then you
entered crazy values here.
|13. Now you can select the
various levels and layers.
- For RESOLUTION, select FULL in most cases. For
global or large regional maps, go down the list as needed
- For SHORELINE TYPES, pick what you want
- For RIVERS, pick what you want
- For POLITICAL BOUNDARIES, you can select anything you want,
but if you are primarily interested in the accuracy and completeness of
the political boundaries, then don't use this exercise, but instead go
Administrative Boundaries and Coastline to a Project Map in Saga.
The coastline there is very very similar to this one.
Then click OK to plot the map.
|14. After a short wait, this
|15. There are navigation and
editing tools along the top. Go ahead and explore how they work.
Each time you make a change, then you'll go right back to Panel 15 to make
the plotting choices again.
|16. Here's an example of
extreme enlargement of the southern tip of Liberia. You can see that
the shoreline (blue) is much more highly resolved than the river (red).
They are from different sources (WVS for the shore; WDBII for the river) so
this isn't really a surprise.
|17. Now use the enlarge tool
(plus sign) to go back to the original Liberia limits.
|18. To save the data for use
in a GIS, select FILE > SAVE AS to get this selection window. For most
purposes, you'll probably want a shapefile, so make that select and click
|19. Navigate to PRODUCTS > GEODASNG and save the results with the filename
You will discover that
GEODAS-NG saves the results as two separate shapes. You can change
their names as follows:
|20. To check on the products,
you can run Saga and use FILE > LOAD > SHAPE, then ADD TO MAP to see them.
The shoreline is red and the rivers are green, but you can choose any colors
you want in the SETTINGS on the right.
|21. It was mentioned above
that there is a different format of output that might be useful. We'll
look at how to get it in the next panel.
|22. Instead of the shapefile
output, you can select the X,Y,ZERO output, as you see here.
- The file has a leading space on each row (bad programming) so it has
to be edited in Excel to remove these spaces.
- Also while working in Excel, it's best to convert the table to
TAB-SEPARATED, for easiest use in many programs (e.g. Saga)
If you have bathymetry data in X, Y, Z format, where Z is the depth, then
you can add the X, Y, 0 file to it. This influences the gridding algorithm
toward exact zero values at the correct shore location, but it is not
guaranteed this will be completely successful.
The shoreline data and the bathy
survey data should come from the same source to have a good chance of
|23. This new version of GEODAS is an excellent tool for your marine data management. Take the
time to read the descriptions of the other stand-alone programs besides the