Continuity mistake: Before Kara uses her heat vision against Vartox she gets some dust on her suit, then she stands up and the dust is gone.
Continuity mistake: When Vartox starts to fight Kara the sun changes between shots.
Continuity mistake: When Vartox attacks Kara from behind the background changes in the next shot.
Continuity mistake: While Kara is fighting Reactron at the junk yard the sun on the floor keeps changing.
Continuity mistake: Livewire has part of her hair over the front of her right shoulder. A shot later after discovering her powers suddenly her hair's over the front of both shoulders.
Continuity mistake: When Alex brings donuts to try to convince Kara to come back to the D.E.O., Kara picks up 2 donuts which suddenly change to 1 once she sits down, and then back to 2 a few shots later in a wide shot.
Continuity mistake: When Cat is on the talk show, the microphone on her collar keeps disappearing and reappearing between shots.
Continuity mistake: While Kara and Alex are on the beach the sun on the floor changes between shots.
Continuity mistake: The bottom circle on the left drawn by Barry on the whiteboard changes shape between shots.
Continuity mistake: While Kara is on the ground after livewire hits her with electricity, the sun changes between shots.
Answer: For one, it's usually cheaper to film in Vancouver because of the tax breaks. But all the CW Arrowverse shows (with the exception of "Black Lighting") are/were filmed in Vancouver. So it makes it easier and cheaper for sharing set designs, crossovers, etc ("Black Lightning" filmed in Vancouver during its crossover). Originally "Supergirl" wasn't part of the Arrowverse when it was on CBS, but it was too expensive to produce and wasn't reaching the wider audience the CW shows had. So CBS moved it to its sister company, The CW.
Bishop73