mongodb-lectures/11. GEO_SPACIAL.md

# Mongo - GeoSpacial

## Lesson Objectives
1. Explain GeoSpacial
1. Explain GeoJSON
1. Explain containers
1. Explain How To Create an Index
1. Explain $near
1. Explain $geoWithin
1. Explain $geoIntersects

## Explain GeoSpacial

## Explain GeoJSON
1. `{ type: "<GeoJSON type>" , coordinates: <coordinates> }`
1. Always list coordinates in `longitude`, `latitude` order.
1. point
	- `{ type: "Point", coordinates: [ 40, 5 ] }`
1. line
	- `{ type: "LineString", coordinates: [ [ 40, 5 ], [ 41, 6 ] ] }`
1. polygons
	- array of coordinate arrays (rings)
		- at least four points and have same start/end position
		- one outer ring and 0+ inner rings
		- cannot self intersect
	- single ring
		- `{ type: "Polygon", coordinates: [ [ [ 0 , 0 ] , [ 3 , 6 ] , [ 6 , 1 ] , [ 0 , 0  ] ] ] }`
	- multiple rings
		- 1st ring is outer ring
		- Any interior ring must be entirely contained by the outer ring
		- Interior rings cannot intersect or overlap each other
		- Interior rings cannot share an edge.
		- http://docs.mongodb.org/manual/_images/index-2dsphere-polygon-with-ring.png
		```
		{
		  type : "Polygon",
		  coordinates : [
		     [ [ 0 , 0 ] , [ 3 , 6 ] , [ 6 , 1 ] , [ 0 , 0 ] ],
		     [ [ 2 , 2 ] , [ 3 , 3 ] , [ 4 , 2 ] , [ 2 , 2 ] ]
		  ]
		}
		```

## Explain containers
1. MultiPoint
```
{
  type: "MultiPoint",
  coordinates: [
     [ -73.9580, 40.8003 ],
     [ -73.9498, 40.7968 ],
     [ -73.9737, 40.7648 ],
     [ -73.9814, 40.7681 ]
  ]
}
```
1. MultiLineString
```
{
  type: "MultiLineString",
  coordinates: [
     [ [ -73.96943, 40.78519 ], [ -73.96082, 40.78095 ] ],
     [ [ -73.96415, 40.79229 ], [ -73.95544, 40.78854 ] ],
     [ [ -73.97162, 40.78205 ], [ -73.96374, 40.77715 ] ],
     [ [ -73.97880, 40.77247 ], [ -73.97036, 40.76811 ] ]
  ]
}
```
1. MultiPolygon
```
{
  type: "MultiPolygon",
  coordinates: [
     [ [ [ -73.958, 40.8003 ], [ -73.9498, 40.7968 ], [ -73.9737, 40.7648 ], [ -73.9814, 40.7681 ], [ -73.958, 40.8003 ] ] ],
     [ [ [ -73.958, 40.8003 ], [ -73.9498, 40.7968 ], [ -73.9737, 40.7648 ], [ -73.958, 40.8003 ] ] ]
  ]
}
```
1. GeometryCollection
```
{
  type: "GeometryCollection",
  geometries: [
     {
       type: "MultiPoint",
       coordinates: [
          [ -73.9580, 40.8003 ],
          [ -73.9498, 40.7968 ],
          [ -73.9737, 40.7648 ],
          [ -73.9814, 40.7681 ]
       ]
     },
     {
       type: "MultiLineString",
       coordinates: [
          [ [ -73.96943, 40.78519 ], [ -73.96082, 40.78095 ] ],
          [ [ -73.96415, 40.79229 ], [ -73.95544, 40.78854 ] ],
          [ [ -73.97162, 40.78205 ], [ -73.96374, 40.77715 ] ],
          [ [ -73.97880, 40.77247 ], [ -73.97036, 40.76811 ] ]
       ]
     }
  ]
}
```

## Explain How To Create an Index
1. `db.collection.createIndex( { <location field> : "2dsphere" } )`

## Explain $near
```
db.test_data.insert({name: 'north', position : { type: "Point", coordinates: [0,1] } });
db.test_data.insert({name: 'east', position : { type: "Point", coordinates: [1,0] } });
db.test_data.insert({name: 'south', position : { type: "Point", coordinates: [0,-1] } });
db.test_data.insert({name: 'west', position : { type: "Point", coordinates: [-1,0] } });
db.test_data.createIndex({position: "2dsphere"});

db.test_data.find({ 
	position: {  
		$near : { 
			$geometry: { 
				type: "Point",
				coordinates: [ 2, 0 ] 
			},
			$minDistance: 0,
			$maxDistance: 200000
		}
	}
});
```

## Explain $geoWithin
```
db.test_data.find({
	position: {
		$geoWithin: {
			$geometry: {
				type : "Polygon" ,
				coordinates: [[ 
					[ 0.5, 0.5 ], 
					[ 1.5, 0.5 ], 
					[ 1.5, -0.5 ], 
					[ 0.5, -0.5 ],
					[ 0.5, 0.5 ], // VERY IMPORTANT
				]]
			}
		}
	}
});
```
## Explain $geoIntersects
```
db.test_data.insert({ name : 'line' , "position" : { "type" : "LineString", "coordinates" : [ [1,0], [2,0] ] } } );
WriteResult({ "nInserted" : 1 });

db.test_data.find({
	position: {
		$geoIntersects: {
			$geometry: {
				type : "Polygon" ,
				coordinates: [[ 
					[ 0.5, 0.5 ], 
					[ 1.5, 0.5 ], 
					[ 1.5, -0.5 ], 
					[ 0.5, -0.5 ],
					[ 0.5, 0.5 ], // VERY IMPORTANT
				]]
			}
		}
	}
});
```