## What is the difference between polygon and MultiPolygon?

A MultiPolygon is a MultiSurface whose elements are Polygons. The interior of a MultiPolygon with more than 1 Polygon is not connected; the number of connected components of the interior of a MultiPolygon is equal to the number of Polygons in the MultiPolygon.

**What is a multi polygon?**

A MULTIPOLYGON is a collection of Polygons. MultiPolygons are useful for gathering a group of Polygons into one geometry. For example, you may want to gather the Polygons denoting a group of properties in a particular municipality.

**How do you change geometry type in PostGIS?**

For PostGIS 2. x, you can use the ALTER TABLE DDL using an expression. To convert from a single-part to multi-part geometry, use ST_Multi: ALTER TABLE my_table ALTER COLUMN geom TYPE geometry(MultiPoint,4326) USING ST_Multi(geom);

### How much tables does PostGIS requires to track and report on geometry types available in spatial database?

In conformance with the Simple Features for SQL (SFSQL) specification, PostGIS provides two tables to track and report on the geometry types available in a given database.

**What is GeoJSON object?**

Introduction GeoJSON is a format for encoding a variety of geographic data structures using JavaScript Object Notation (JSON) [RFC7159]. A GeoJSON object may represent a region of space (a Geometry), a spatially bounded entity (a Feature), or a list of Features (a FeatureCollection).

**How do you convert a MultiPolygon to a polygon in Python?**

2 Answers

- extract the outer boundary of individual components of the MultiPolygon of interest.
- expand-shrink each of the outer boundaries in order to fill “holes” which these boundaries approximately encompass, e.g., to handle a “doughnut with a cut”
- merge all geometries obtained in previous step.

#### What Srid 0?

SRID 0 represents an infinite flat Cartesian plane with no units assigned to its axes. In the future, computations may use the specified SRID values. To ensure SRID 0 behavior, create geometry values using SRID 0. SRID 0 is the default for new geometry values if no SRID is specified.

**What is a geometry column?**

Adding and Populating a Geometry Column. PostGIS stores a table’s spatial information in geometry columns. Usually these columns have the word “geom” floating around in their name. If you select * on a table with a geometry column, the geom column will look like a long series of nonsense.

**What is PostGIS extension?**

PostGIS is an open source, freely available, and fairly OGC compliant spatial database extender for the PostgreSQL Database Management System. In a nutshell it adds spatial functions such as distance, area, union, intersection, and specialty geometry data types to the database.

## Is GeoJSON better than KML?

KML is similar to GeoJSON and can store points, lines, polygons, and other vector data. Unlike GeoJSON, it’s based on XML rather than JSON. It is important to note that when you create a KML file, the additional custom attributes go into an element.

**Is GeoJSON a vector?**

GeoJSON is an open specification for text representation of vector spatial data layer. GeoJSON files can easily be hosted on static websites and can be directly read by GIS tools.

**What is Unary_union?**

According to the GEOS docs, the library that Shapely is a wrapper around, unary_union splits a single LineString into separate LineString objects by self-intersection points.

### Is it possible to import a shape file containing multipolygons in PostGIS?

Is it possible to import a shape file containing multipolygons into single polygon in PostGIS? Whenever I try importing a shape file of a polygon, it is stored as a multipolygon (as opposed to a single polygon) in a geom column.

**How to create a polygon geometry in PostGIS?**

Here are some highlights of Polygon functions in PostGIS: ST_MakePolygon, ST_Polygon, ST_PolygonFromText → To create a Polygon Geometry. ST_ExteriorRing → Returns a line string representing the exterior ring of the POLYGON geometry.

**How is multipolygon geometry different from multisurface geometry?**

Each interior boundary defines a hole in the Polygon whereas multi polygon is multisurface whose elements are polygons. Let’s assume that we have a table which contains multi polygon geometry data. Now we have to extract geometry of each polygon from multipolygon geometry and have to dump the same into a separate table.

#### How to convert multipolygon to single in PostgreSQL?

I used ST_DUMP to convert a table of multipolygon geometries in PostgreSQL to a new table with polygon geometries and other columns of data. Update: I think this could be accomplished much easier with this query.