Project 1 Solution

  1. …\Project1_harbor_2018\Project1.aprx
  2. Add Data
    1. load the excel data tab with the Hg values from the project folder into ArcGIS (as a table).
    2. …\DEQ_dissolved_metals_2016.xlsx\edited4ArcGIS$
  3. Possible wrong turn: Although that might be easiest, you can’t join the water quality measurements in the excel table to the “DEQ_sampling_sites_2016” feature class because it keeps only the first record with each station.  If you do it this way, you only wind up with 111 samples instead of 239; it appears that it only takes the first one.
    vs the same table joined to the DEQ sampling stations feature class
  4. Instead, we load the points directly using the latitude and longitude fields in the edited4ArcGIS$ table
    1. Use the “add data” button in the Map tab, or right  click on the table and “Display XY data.”
    2. use longitude for x and latitude for y, and I defined the coordinate system to be NAD 1983 (which is a guess in this case because the web site doesn’t say).
    3. Then, to make it permanent, you need to export the data (right click on new layer, choose data, and export) or use Copy Features tool.which I saved as \Project1.gdb\Samples_2016
    4. I then deleted all the fields I didn’t need for simplicity (or you could just turn them off to keep all the data, but get it out of the way).
  5. By plotting them as open circles that vary in size, you can see that multiple samples come from one place. Labeling helps too.
  6. Next you have to limit the analysis of the samples to just the streams.  I used a definition query to do that (and again, you could also save this out to a new feature class if desired).This leaves 239 sample points at fewer locations.
  7. To bring in the watersheds, I chose the “Add data” button and search the “living atlas” for “HUC_6” features, drilled down and double-clicked the layer.
  8. To select the Virginia basins, I also added a “states” layer from the “Living Atlas,” selected Virginia in the attribute table, and used the “Select by location” tool in the Map tab to find the features that intersected Virginia.
  9. You could also have selected the basins that CONTAIN sample points.  Either way.
  10. Export those selected HUC_6 basins to a feature class (it is too big to work with as an online database) by right-clicking on the layer and choosing data\export features
    …. \Project1.gdb\VA_HUC6_basin
  11. Some of the basins touch Virginia, but aren’t really in VA and don’t have any samples in them, but they will come out in the spatial join.
  12. Now that we have sample data for Hg in one feature class and basins in another, we can execute spatial join (3 times) for the minimum, maximum and average Hg value within the basin.
  13. Labeled the polygons according to their value + “ μg/l Hg” and the basin name

    or just a number with  a “halo” to see against the darker symbols.MAXIMUM below

    MEAN below
  14. Now ready to display the data in a Layout. See layout comments on the “what to open” page for Feb 14th.