perimeter

Perimeter of polygon shape in geographic or planar coordinates

Since R2024a

Syntax

P = perimeter(shape)

Description

P = perimeter(shape) calculates the perimeter of a polygon shape, which is the sum of the lengths of its boundaries.

Examples

Calculate Perimeter of Polygon in Geographic Coordinates

Read worldwide land masses into the workspace as a geospatial table. Extract the polygon shapes.

land = readgeotable("landareas.shp");
shape = land.Shape

shape=537×1 geopolyshape array with properties:
              NumRegions: [537x1 double]
                NumHoles: [537x1 double]
                Geometry: "polygon"
    CoordinateSystemType: "geographic"
           GeographicCRS: [1x1 geocrs]
      ⋮

Calculate the perimeters of the polygon shapes.

P = perimeter(shape);

The units depend on the geographic coordinate reference system (CRS) for the shape. Find the length unit for the geographic CRS. The result indicates that the perimeters are in meters.

shape.GeographicCRS.Spheroid.LengthUnit

ans = 
'meter'

Include the perimeters in the geospatial table by creating a new table variable. Sort the rows of the table in descending order by Perimeter. Then, view the first eight rows of the table by using the head function.

land.Perimeter = P;
land = sortrows(land,"Perimeter","descend");
head(land)

       Shape                  Name               Perimeter 
    ____________    _________________________    __________

    geopolyshape    "Africa and Eurasia"         1.4207e+08
    geopolyshape    "North and South America"    9.9316e+07
    geopolyshape    "Antarctica"                 3.0741e+07
    geopolyshape    "Australia"                  1.7029e+07
    geopolyshape    "Greenland"                   1.281e+07
    geopolyshape    "Baffin Island"              9.2117e+06
    geopolyshape    "New Guinea"                 7.2776e+06
    geopolyshape    "Borneo"                     4.9742e+06

Calculate Perimeter of Polygon in Planar Coordinates

Read hydrographic data for Concord, MA into the workspace as a geospatial table. Extract the polygon shapes.

hydro = readgeotable("concord_hydro_area.shp");
shape = hydro.Shape

shape=98×1 mappolyshape array with properties:
              NumRegions: [98x1 double]
                NumHoles: [98x1 double]
                Geometry: "polygon"
    CoordinateSystemType: "planar"
            ProjectedCRS: [1x1 projcrs]
      ⋮

Calculate the perimeters of the polygon shapes.

P = perimeter(shape);

The units depend on the projected coordinate reference system (CRS) for the shape. Find the length unit for the projected CRS. The result indicates that the perimeters are in meters.

shape.ProjectedCRS.LengthUnit

ans = 
"meter"

Create a new geospatial table from the shape objects and the perimeters. View the first eight rows of the table by using the head function.

hydro_perimeter = table(shape,P,VariableNames=["Shape","Perimeter"]);
head(hydro_perimeter)

       Shape        Perimeter
    ____________    _________

    mappolyshape     289.22  
    mappolyshape      11264  
    mappolyshape     207.37  
    mappolyshape     117.55  
    mappolyshape     633.93  
    mappolyshape     370.54  
    mappolyshape     3378.7  
    mappolyshape     1650.6  

Input Arguments

shape — Polygon shape

geopolyshape object | mappolyshape object | array of geopolyshape objects | array of mappolyshape objects

Polygon shape, specified as a geopolyshape object, a mappolyshape object, an array of geopolyshape objects, or an array of mappolyshape objects.

Output Arguments

P — Perimeter

array

Perimeter, returned as an array. The size of P matches the size of shape.

The units of P depend on the type of polygon shape.

• When shape contains geopolyshape objects, the length unit of the reference ellipsoid for the shape determines the units. To find the length unit, get the geocrs object for the shape by querying the GeographicCRS property of the shape object. Then, get the ellipsoid by querying the Spheroid property of the geocrs object. If the ellipsoid is a referenceEllipsoid or referenceSphere object, then query the LengthUnit property of the ellipsoid. For a shape shp, the length unit is shp.GeographicCRS.Spheroid.LengthUnit. If the GeographicCRS property of the object is empty, the function calculates the perimeter using the WGS84 reference ellipsoid and a length unit of meters.

• When shape contains mappolyshape objects, the length unit of the projected coordinate reference system for the shape determines the units. To find the length unit, get the projcrs object for the shape by querying the ProjectedCRS property of the shape object. Then, query the LengthUnit property of the projcrs object. For a shape shp, the length unit is shp.ProjectedCRS.LengthUnit.

When shape contains geopolyshape objects, the perimeter function calculates the perimeters using geodesics.

Tips

The accuracy of the perimeter function depends on the resolution of the data used to create the polygons. As a result, the function can return different results when you use polygon shapes from different data sets as inputs. This image compares the perimeters of polygon shapes for the state of Florida from two data sets.

Version History

Introduced in R2024a