How do you calculate the area of a polygon in GIS?

First, you need to ensure that the layer containing the polygon is in right coordinate system. That is, coordinate system measured in meters. Then you compute area with the "Calculate geometry" function within the attribute table of the layer.

You can calculate the area of a polygon in GIS using Python by using the Shapely library, but make sure you set the crs before you go with this process. install shapely for your notebook or code terminal read the feature and calculate area variable = polygon.area should provide you area in square meters. Hope this will be helpful

I check the coordinate system and then I add a new field in the attribute table. I am working with Qgis and it provides the function $area, so in the new field I open the field calculator, type $area and the polygon’s / polygons’ area is calculated.

Few Examples 1. Land Use Planning: Example: In urban planning, calculating the area of different land use zones (residential, commercial, industrial) helps in determining the distribution of resources, infrastructure needs, and population density. 2. Infrastructure Development: Example: Civil engineers and urban developers use GIS to calculate areas for infrastructure projects like roads, bridges, and reservoirs. Accurate area calculations are crucial for budgeting, materials estimation, and project planning. 3. Real Estate and Property Management: Example: For valuation purposes, site suitability analysis, and land parcel delineation. Accurate area calculations are essential for property transactions and legal documentation.

First of All Ensure that Polygon layer coordinate system is Projected then second step is , just run calculate geometry Function within the attribute table of that layer .

Cartographic projection affects area calculation the most. Equal-area (equivalent) projections should be used, and area should be mapped in a large scale. An extreme example of area distortion is Grenland on a global scale Web Mercator Map, which appears larger than Africa. Areas should be calculated in projected coordinate systems (CRS) that use metric units, because calculations on an ellipsoid are much more complicated, and their original result would be in angular units (which are meaningless). Dataset resolution also affects area calculation, because higher precision of boundaries at large scales gives more accurate results.

Le calcul de la surface peut être influencé par plusieurs facteurs comme projection (chaque projection cartographique a ses propres distorsions inhérentes, ce qui peut affecter les calculs de surface), résolution des données(la taille des pixels dans le cas des images raster ou la densité des points dans les vecteurs), topologie (des erreurs topologiques comme les polygones qui se chevauchent ou les trous non intentionnels), modélisation du Terrain(les zones avec des reliefs significatifs ou 3D modélisation est plus efficace), échelle de travail(Les détails fins peuvent être visibles à une échelle plus grande mais se perdent à une échelle plus petite).

First of all how the area calculation will be performed will depend of you project objetives. If it is a critical value it will depend of the scale of the cartographic data and projections. If it not just look for a equivalent projection (it is also have its limits) and perform a calculation using standard procedures like get $area, st_area(geometry), and others. Take in account these calculations are made in the cartesian space.

Choosing the right map projection for calculating the area of a polygon (or any other GIS analysis for that matter) can be intimidating. However, these two tips will help you out most of the time: 1. Use the Web Mercator projection (EPSG:3857) if your study area covers a very large area such as a country or larger. 2. Use the UTM projection if your polygon is small such as a state, province or local government. This is because the UTM projection divides the earth into small squares called UTM zones. The right EPSG code for you depends on the UTM zone your polygon falls in. For example, southwestern Nigeria falls in UTM zone 31N which has an EPSG code of 26331.

The other factor might be elevation scale factor as well as projection scale . In the now 3d GIS WORLD, the elevation of the polygon with a vertical datume applied, will affect the area, since the elevation scale affects the length of the sides. A polygon at 1000' above sea level is going to be larger than the same polygon drawn at sea level. Large area polygons will be affected much more by this because of the much longer sides.

Your choice of a projected coordinate system depends on many factors, including the part of the world you are mapping, the scale of your map, and the purpose of your map. You want to choose a projected coordinate system in which the places and properties that are most important to your map are the least distorted.

Through steps bellow we can calculate polygon area - Add new field and choose "double or float" for data type - In calculate geometry screen select coordinate system & unit depend on your scale of study area

Open the GIS app and load the data containing the polygons that you want to measure and or select starting point if getting live measurements. Select the Measure Area tool in the Advanced Digitizing toolbar. Click on the polygon whose area you want to measure. The area will be displayed in the Measurements panel.

Slight overlap w/comment below: use Field Calculator. One more issue: in QGIS (perhaps also ArcGIS?), the layer actually needs to be projected into the correct CRS. You cannot just switch the workspace/dataframe to that CRS to do the calculation on a layer in which the underlying data not projected into the desired CRS. You need to make sure the actual data is projected to meters or feet in the projection/datum you desire.

Make sure your polygon layer is in a projected coordinate system that uses meters as the unit of measurement. Commonly used systems include UTM and State Plane coordinate systems, which are measured in meters at a regional or local scale. If your data is in a geographic coordinate system (latitude and longitude), you might need to project it to a suitable projected coordinate system before calculating area. Open the attribute table of the polygon layer in your GIS software. In ArcGIS, this function is available when you right-click the field heading in the attribute table and select "Calculate Geometry." Within the "Calculate Geometry" dialog box, select the option to calculate area. Ensure you specify that the desired unit

Pour déterminer la superficie d'un polygone via les attributs dans QGIS, le "Calculateur de champs" qui permet d'intégrer ou de mettre à jour une colonne avec les données de superficie. En accédant à la table d'attributs, activez le "Calculateur de champs". Pour consigner la superficie, vous pouvez soit opter pour la création d'une nouvelle colonne, par exemple "Surface", soit actualiser une colonne préexistante. Lors de la sélection du format, optez pour "decimal real", et définissez, si nécessaire, la longueur et la précision. Dans la section formule, utilisez `$area` ou `area($geometry)`. Enfin, validez avec "OK" pour procéder au calcul. Ainsi, chaque polygone sera attribué d'une valeur de superficie dans la colonne désignée.

using SQL-mm could be st_area(geometry), a more complex will be st_area(tranform(geometry, 'any equal area projection EPSG code')). Sometimes some softwares calculate area by default or can be calculated using a FieldCalculator like in ArcGIS or QGIS. BUT be care because not all area calculations are valid. It depends of the cartographic projection.

In general, use the Field Calculator in the Attribute Table to simultaneously calculate the area of all polygons in a layer. In QGIS you can just choose the Information (i) tool to get data on one polygon, but to generate a persistent record of the area-calculations use the Field Calculator. As you set up the SQL function in the calculator, you can also include conversion calculations at the same time. 1 acre = 43560 square feet, BTW.

arcpy code: # Set the workspace arcpy.env.workspace = r"C:\Path\To\Your\Workspace.gdb" # Iterate through feature classes feature_classes = arcpy.ListFeatureClasses() for fc in feature_classes: # Add a new field for area arcpy.AddField_management(fc, "Area", "DOUBLE") # Calculate the area arcpy.CalculateField_management(fc, "Area", "!shape.area!", "PYTHON")

To calculate the area of a polygon in GIS, you typically use the "Calculate Geometry" function within the attribute table of your polygon layer, where you select the "Area" property to automatically generate an area value for each polygon feature, based on the chosen units of measurement in your coordinate system; this is usually done in software like ArcGIS or QGIS.

PostGIS makes it easy to calculate areas and distances, but you need to be careful of your types and projections. You need to use a geography data type which requires a lat/long input (SRID 4326). You can test this by drawing a great circle polygon from the North pole, to the equatorial IDL to the South pole to the equatorial prime meridian, and then multiplying the half-planet by 2. This code: select st_area(('SRID=4326;POLYGON((0 90, 180 0, 0 -90, 0 0, 0 90))'::geometry)::geography) * 2.0; ...results in 510,065,621,724,088.56 m2 or: 510,065,621 km2. This is pretty close to: 510,064,472 km2 that you get if you do a web search for the surface area of the Earth.

étant un grand amateur de QGIS, j'préfère particulièrement la solution offerte par PyQGIS. On a la possibilité de rédiger des scripts Python directement via la Console Python de QGIS et de les exécuter, permettant ainsi de créer, de calculer ou de mettre à jour les polygones directement dans QGIS et également dans la base de données associée. Une alternative serait d'utiliser les actions liées au style de couche qui supportent l'exécution de code Python via PyQGIS. Voici un simple exemple de code pour estimer la superficie d'un polygone : layer = iface.activeLayer() for feature in layer.getFeatures(): geom = feature.geometry() print(f"Polygon ID {feature.id()}: Area = {geom.area()} m2")

Indeed selecting a right project for you project or study area is primary and most important thing to do in GIS. If you are comparing area of multiple polygon files for same study area, make sure all files are in a common projection system.

The area calculation method will depends of the project's aims.In cadastral surveying the area calculation precision and error could be critical, but in other disciplines like demographics could be resolved using any equal area or other projection where the deformation will be not significative.