ignore csv rows where lat or lng are empty

[derekeder]

currently, the app will throw an error if one of your rows is missing latitude or longitude values. we should instead skip these rows.

[aliceell]

any progress on this? i have a dataset with a not-inconsiderable number of rows with blank lat/longs. i'm looking into how to get the code to skip those rows (maybe by editing one of the functions in csv-to-geojson?) but haven't figured out a good solution yet...