How do I cut down polygons to only the extent of another polygon?

[EllenWildig]

Basically my brain has taken a leave of absence and won't help me out. I've attached a screenshot of my work so far. I want the mint green polygons to only extend as far as the DEM, which has another transparent polygon drawn over the top of it. How do I go about doing this, essentially the DEM is the maximum extent of my model, (those purple lines and I'm only interested in the city they affect within that zone.

Also as an aside, if anyone knows where I can get concise census data for Tacoma and/or land use breakdowns for the urban area that would be greatly appreciated.

Thanks

[DanPatterson_Retired · Accepted solution]

Clip the polygons to the desired extent if that is critical.  It is fast and guaranteed to work

[EllenWildig]

Thank you so much, I knew there was an easy answer. I am literally half asleep in the library. I'm in the UK so we're about to cross onto the wrong side of midnight

[DanPatterson_Retired]

no problem...you probably wouldn't have slept anyway, if you hadn't wrapped it up