What is Geographic Information System?

Geographic Map Data

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Map Analysis and Queries

What is Geospatial?

• If we summarise GIS and GeoSpatial, geo spatial is GIS - the whole map data.

Only Map Analysis and Queries

Spatial Reference System ID (SRID)

• Measuring unit for geometry types.

• It specifies which units (degrees/metres) are going to be used to represent the geometry types.

• We are going to use SRID 4326

  Bengaluru/ Coordinates

  8637791 m, 1456487 m

  Bengaluru/ Coordinates

  12.9716 °N, 77.5946 °E

...a small caveat

• Longitude is x

• Latitude is y

• ...not the other way around

(30°,15°)

(x,   y)

(lat, long)

Geometries Representations

GeoJson

Geographic Mark-up Language

Well Known Text (WKT)

GeoJson

Geographic Mark-up Language

Well Known Text (WKT)

Point as GeoJson

e.g. GeekyAnts On Maps

Linestring as GeoJson

e.g. route along road between two points

Polygon as GeoJson

e.g. an area of sub-locality of BTM

GEOS Functions

1 .contains

• Checks if a geometry is inside another geometry.

• Invoked as polygon.contains(point)

GEOS methods & properties

2 .distance

• Returns the distance between the closest point in this geometry and the other geometry

• Invoked as polygon.distance(point)

GIS ORM

• Extends Django ORM

• Provides spatial lookup and queries

• Takes advantages of database procedures by postgis and others

Retrieve factories which covers a given point

Using GEOS API

Using ORM

GEOS API would have to collect all rows of database in memory

GIS ORM would do the query right in database. Thus, efficient.

GIS ORM (QuerySet) API Ops

contains

intersects

More GIS ORM Ops

• overlaps

• bboverlaps

• bbcontains

• etc.

PROS

1. Fully supports GIS Standards

2. Provides Spatial ORM

3. Low learning curve

4. Plug & Play nature

CONS

1. Is overkill if geometries do not have to be stored

2. Has limited support for MySQL