Saturday 29 December 2018

Challenger Expedition DIY Web Map

[Update: Spilhaus video here c/w DIY add-your-own image on eve of 150th anniversary]

The last two blogposts showed how to create correct polar maps in ArcGIS and QGIS here from publicly posted class notes blogged.

Let's look at now creating complete maps in AGOL from publicly available data, and analyzing it over time to see their historic significance. This results in this web map of the HMS Challenger 1873-1876 Expedition:

  1. Google and find HMSChallenger-Station-Data on this fan site or grab it directly on Dropbox - you can see the metadata by clicking About on the web map in the second panel above, or directly here - note there are other sources, but raw location data is often in separate columns: degrees, minutes and seconds, whreas this is in decimal longitude (X) & decimal latitude (Y)
  2. Log into an AGOL account - you can get a free login, and at 500 points you won't exceed the 1,000 point free limit - create a map and add tags and description from Wikipedia
  3. Change the based map to Oceans, which is the latest from Esri's excellent Living Atlas  series that show the ocean bathymetry brilliantly
  4. Click Add Layer from File and select CSV:
    a. save Excel files as CSV file if you downloaded it - in Dropbox file ends with _redux
    b. remove temp. at depth... columns at far right, as they're read as duplicates by AGOL
    c. bulk-replace spaces and "/"  with "_" (underscore) to make file importable by AGOL
  5. d. Split, reorder and merge dd/mm/yyyy dates to mm/dd/yyyy format legible by AGOL 
  6. Fine-tune the map display:
    a. choose Depth_(fathoms) as attribute to show
    b. while Counts and Amounts (size) may work for you,  select the same by (color) to make depths more legible (the default white-to-blue works quite well)
    c. remember to select Done to save changes, and Save the map you just created
This will yield a static map with all Station Data. We can time-enable this map by activating the time (Year) column: this allows to view the ship's progress by month across the oceans. But for that we most host the spreadsheet data on AGOL: follow Publish a CSV File instructions and then:
  1.  In AGOL go to Contents and select the Feature Layer (hosted) you just created 
  2. Under Layers select Time settings and select the drop down  Year 
  3. Save and Open in Map Viewer, styling it the same as above.
Voilà! You have a dynamic map, where you can follow the deep soundings in the dark beiges - especially Marianas Trench along the date line, where Challenger Deep was named after this - and shallower ones in light beiges - the last two animation points are the Mid Atlantic Ridge, which this expedition is credited with discovering.
This exercise shows you how to host and style complete datasets in ArcGIS Online... As in previous posts, we trust this will inspire you to craft your own maps... and help your particular areas of interest!    

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