Isolating points by handdrawn polyline, testing for containment and pattern culling?

so i downloaded an osm file which is a rectangular chunk by nature. lets say i only need the data (to calculate the ratio of the length of "highway" to "oneway") of a specific district and i want to throw away the rest.

ive drawn a polyline (boundary of the district) in rhino, tested all points for containment inside the curve and then culled them by pattern.

im getting: solution exeption: Object reference not set to an instance of an object

any thought, ideas? can i simply crop points or does the data get broken somehow? am i on the right path?