Sequence and Series....
"Series are generally thematically related or connected while Sequences are based on causal relationships."
Nathan Lyons, from Landscape as Photograph (1985)
Parking Lots. Ed Ruscha
East of Lancaster. Robbert Flick
The traditional concept of Sequence tends to go much deeper than simply having a causal relationship. Stieglitz firmly believed in the value of multiple images bound by context serving to support one another and producing a more complex and complete document than a single image was capable of providing. Minor White expanded on this concept by going beyond the pure visual connections of sequential images and moving into a spiritual and mystical connection that have roots in the mixed media of photography and poetry.
With that in mind, it becomes easier to distinguish between Ruscha's series of Parking Lot's and Flick's sequence of Landscapes. I've always loved Ruscha's work, as well as other masters of the series genre such as Bernd & Hilla Becher, but I tend to prefer the visual poetry of sequences that is clearly a part of Flick's work.