2.33 GSHHG Vectors
 

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2.33 Managing Global Coastline, River and Lake Vectors: GSHHG

  • Exercise Title:  Managing Global Coastline, River and Lake Vectors: Global Self-Consistent, Hierarchical, High-Resolution Geography Database (GSHHG)

  • 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):

  • Required Software:

  • Other Resources: 

  • Author:  Murray Brown

  • Version:  8-5-2014

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 detailed GADM administrative borders and the VLIMAR marine boundaries, the last section ("BORDERS") is of lesser interest.

"The geography data come in five resolutions:

  1. Full resolution: Original (full) data resolution.

  2. High resolution: About 80 % reduction in size and quality.

  3. Intermediate resolution: Another ~80 % reduction.

  4. Low resolution: Another ~80 % reduction.

  5. Crude resolution: Another ~80 % reduction.

Unlike the shoreline polygons at all resolutions, the lower resolution rivers are not guaranteed to be free of intersections.


SHORELINES are furthermore organized into 6 hierarchical levels:

  1. L1: boundary between land and ocean, except Antarctica.

  2. L2: boundary between lake and land.

  3. L3: boundary between island-in-lake and lake.

  4. L4: boundary between pond-in-island and island.

  5. L5: boundary between Antarctica ice and ocean.

  6. L6: boundary between Antarctica grounding-line and ocean.

RIVERS are organized into 10 classification levels:

  1. L0: Double-lined rivers (river-lakes).

  2. L1: Permanent major rivers.

  3. L2: Additional major rivers.

  4. L3: Additional rivers.

  5. L4: Minor rivers.

  6. L5: Intermittent rivers - major.

  7. L6: Intermittent rivers - additional.

  8. L7: Intermittent rivers - minor.

  9. L8: Major canals.

  10. L9: Minor canals.

  11. L10: Irrigation canals.

BORDERS are organized into three levels (read the special note above about these data):

  1. L1: National boundaries.

  2. L2: State boundaries within the Americas.

  3. L3: Marine 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:
  • GSHHG_SHP
  • WDBII_SHP

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 opens.
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 to 2.8 Adding 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 map appears.
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 OK.
19.  Navigate to PRODUCTS > GEODASNG and save the results with the filename coasts_lakes_rivers_liberia_gshhs_geodasng_full

You will discover that GEODAS-NG saves the results as two separate shapes.  You can change their names as follows:

  • coasts_liberia_gshhg_geodasng_full_shore
  • lakes_rivers_liberia_gshhg_geodasng_river
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 success.

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 Coastline Extractor.