Why is it assumed on sectionals that the area outside of a 700 AGL Class E (Echo) transition area is Class E starting at 1,200 AGL? In this Bold Method article (http://www.boldmethod.com/learn-to-fly/airspace/class-g-airspace/) it is stated that anything beyond the hard lines of this examples 1,200 ft AGL Class E (blue) transition area is Class G (Golf). 

So far so good.



However, further down in the article, it is stated that beyond the hard lines of the magenta 700 ft AGL Class E transition area that the airspace is Class G until 1,200 ft AGL at which point it turns into Class E again (think the blue Class E area that exists above this entire area). 



Why is it assumed that outside the 700 ft AGL Class E transition area there lies 1,200 ft AGL Class E? It surely isn't represented in the screenshot. Couldn't it just as well be Class G until 14,500 ft AGL?
Take a look at the legend on the side of a VFR chart. (You can get them for free at https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/vfr/ )

Class E exists at 1200' AGL unless otherwise designated as shown above.