We're talking about timezones. The whole article is about timezones. The map has no purpose except to show timezones. I cannot emphasize enough the point that timezones are the relevant unit of measurement in this article.

I think the point is that although it's only 1000km, the difference when expressed as a proportion of one day is the same. So noon in LA corresponds to late afternoon in NY, noon on Greenland's west coast corresponds to late afternoon on Greenland's east coast.