Draw GeoJson in Apple Maps as overlay

Question

Can someone tell me how can I draw a GeoJson file as an overlay in apple maps? I want a complete example, I have the shapes as Polygons or MultiPolygons?

This file Countries GeoJSON is enough for me if you provided me with a code or a library to use to render it using MKMapView

Obannon

Answer 1

I've found a solution in case someone wants help too.

@interface HHLViewController

+ (NSArray *)countriesOverlays;

@end

@implementation HHLViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    NSArray *overlays = [HHLViewController countriesOverlays];
    [self.stateMapView addOverlays:overlays];
}

+ (NSArray *)countriesOverlays {
    NSString *fileName = [[NSBundle mainBundle] pathForResource:@"countries" ofType:@"json"];
    NSData *overlayData = [NSData dataWithContentsOfFile:fileName];

    NSArray *countries = [[NSJSONSerialization JSONObjectWithData:overlayData options:NSJSONReadingAllowFragments error:nil] objectForKey:@"features"];

    NSMutableArray *overlays = [NSMutableArray array];

    for (NSDictionary *country in countries) {

        NSDictionary *geometry = country[@"geometry"];
        if ([geometry[@"type"] isEqualToString:@"Polygon"]) {
            MKPolygon *polygon = [HHLViewController overlaysFromPolygons:geometry[@"coordinates"] id:country[@"properties"][@"name"]];
            if (polygon) {
                [overlays addObject:polygon];
            }


        } else if ([geometry[@"type"] isEqualToString:@"MultiPolygon"]){
            for (NSArray *polygonData in geometry[@"coordinates"]) {
                MKPolygon *polygon = [HHLViewController overlaysFromPolygons:polygonData id:country[@"properties"][@"name"]];
                if (polygon) {
                    [overlays addObject:polygon];
                }
            }
        } else {
            NSLog(@"Unsupported type: %@", geometry[@"type"]);
        }
    }

    return overlays;

}

+ (MKPolygon *)overlaysFromPolygons:(NSArray *)polygons id:(NSString *)title
{
    NSMutableArray *interiorPolygons = [NSMutableArray arrayWithCapacity:[polygons count] - 1];
    for (int i = 1; i < [polygons count]; i++) {
        [interiorPolygons addObject:[HHLViewController polygonFromPoints:polygons[i] interiorPolygons:nil]];
    }

    MKPolygon *overlayPolygon = [HHLViewController polygonFromPoints:polygons[0] interiorPolygons:interiorPolygons];
    overlayPolygon.title = title;


    return overlayPolygon;
}

+ (MKPolygon *)polygonFromPoints:(NSArray *)points interiorPolygons:(NSArray *)polygons
{
    NSInteger numberOfCoordinates = [points count];
    CLLocationCoordinate2D *polygonPoints = malloc(numberOfCoordinates * sizeof(CLLocationCoordinate2D));

    NSInteger index = 0;
    for (NSArray *pointArray in points) {
        polygonPoints[index] = CLLocationCoordinate2DMake([pointArray[1] floatValue], [pointArray[0] floatValue]);
        index++;
    }

    MKPolygon *polygon;

    if (polygons) {
        polygon = [MKPolygon polygonWithCoordinates:polygonPoints count:numberOfCoordinates interiorPolygons:polygons];
    } else {
        polygon = [MKPolygon polygonWithCoordinates:polygonPoints count:numberOfCoordinates];
    }
    free(polygonPoints);

    return polygon;
}
@end

Obannon

This won't ever help anybody if you don't tell us what HHLViewController is. – Burkey

@Julian - HHLViewController is the current class - it is only used in the code to refer to the class methods that @Obannon added to construct the overlays. – Village

can i fill the color to specific county.? please help me. – Glandular

Answer 2

I made a some Swift version for MultiPolygon

import Foundation
import MapKit

struct MapGeoGeometry: Codable {
    let type: String
    let coordinates: [[[[Double]]]]
}

struct MapGeoFeature: Codable {
    let type: String
    let geometry: MapGeoGeometry
}

extension MapGeoFeature {

    func toPolygons() -> [MKPolygon] {

        return geometry.coordinates
            .map { data in return data.map { MapGeoFeature.polygon(from: $0) } }
            .reduce([], +)
    }

    static func polygon(from points: [[Double]]) -> MKPolygon {
        let coords = points.map { CLLocationCoordinate2D(latitude: $0[1], longitude: $0[0]) }

        return MKPolygon(coordinates: coords, count: coords.count, interiorPolygons: nil)
    }

}

Broth

Thanks! This was helpful. After getting the [MKPolygon], I had to use MKMapViewDelegate's mapView(_:rendererFor:) to set renderer's stroke color so I could see it on my MKMapView – Fascination