getContextForEnvelope.m

// get voting districts for an area

SGEnvelope *envelope = [SGEnvelope envelopeWithNorth:40.613952
                                                west:-105.90271
                                               south:39.078908
                                                east:-103.513184];

[query setFilters:[NSArray arrayWithObject:SGContextFilterFeatures]];
[query setFeatureCategories:[NSArray arrayWithObjects:SGFeatureCategoryLegislativeDistrict,
                                                      SGFeatureCategorySchoolDistrict,
                                                      nil]];

[client getContextForQuery:query
                  callback:[SGCallback callbackWithSuccessBlock:
                            ^(id response) {
                                // you've got feature polygons!
                                // to create an array of SGFeature objects:
                                NSArray *features = [NSArray arrayWithSGCollection:response
                                                                              type:SGCollectionTypeFeatures];
                            } failureBlock:^(NSError *error) {
                                // handle failure
                            }]];