make bivariate toggle map

[cnell-usgs]

• [x] add basemap svg
• [ ] embed shaded relief as png in background, keep it very light and white
• [x] bind csv data to sites on map using id similar to temp prediction (https://github.com/usgs-makerspace/temperature-prediction/blob/master/src/views/set2/Set2.vue#L1011-L1037)
• [x] use csv data from SNOTEL to map color scales
• [x] create toggleable legend with 2 variables in check boxes
• [ ] create a bivariate color ramp when both are selected
• [x] experiment with data options - peak swe, snow or peak swe date with the second variable being either the diff or anomaly from the historical record

[cnell-usgs]

From these explorations, I have concluded that the bivariate legend may be overcomplicated for the message. Pivoting to make 2 data layers that are anomalies for magnitude and timing.

New tasks:

• [x] add Alaska to map view and SNOTEL sites/data
• [x] add data variable for timing - using SM50 (https://journals.ametsoc.org/view/journals/clim/23/9/2009jcli2951.1.xml#i1520-0442-23-9-2293-f01)
• [ ] set toggles or buttons to "show timing" and "show magnitude" OR explore showing both variables simultaneously with different encodings

[cnell-usgs]

• [x] adjust map sizing on mobile and positioning of toggles/legend/text
• [x] add legend