Reproject Features

Overview

Projection transformation is a core geoprocessing function. It converts geographic data from one coordinate system to another so spatial data from different sources can overlay, analyze, and visualize correctly.

Projection transformation commonly includes:

• Transforming between geographic coordinate systems, such as WGS 84 to CGCS2000.
• Transforming between projected coordinate systems, such as UTM Zone 50N to an Albers equal-area conic projection.
• Transforming between geographic and projected coordinate systems.

Use Cases

Multi-source Data Integration And Overlay Analysis

• Scenario: Data from different sources, such as satellite imagery, GPS points, or administrative boundaries, may use different coordinate systems such as WGS 84, CGCS2000, or Web Mercator.
• Usage: Transform all data to the same coordinate system before accurate spatial overlay analysis, such as buffer analysis or intersect queries.
• Example: Reproject WGS 84 UAV survey data to overlay with cadastral data in a local coordinate system for land-cover change analysis.

Map Production And Visualization

• Scenario: Map production may need to follow regional standards or reduce distortion.
• Usage: Transform data to a projection suitable for the region, such as an Albers equal-area projection for China, to preserve area, shape, or distance as needed.
• Example: Use an equal-area projection when creating a national population density map to avoid area distortion.

Accurate Measurement And Calculation

• Scenario: Length and area cannot be calculated accurately directly in a geographic coordinate system whose unit is degrees.
• Usage: Transform data to a projected coordinate system, usually in meters, before measuring parcel area or road length.
• Example: Reproject urban green-space data to a local projected coordinate system before calculating area.

Remote Sensing And Vector Data Registration

• Scenario: Remote sensing imagery may use its own coordinate system, such as UTM, and needs to align with local vector data.
• Usage: Reproject the imagery or vector data to the target coordinate system.
• Example: Align Landsat imagery in UTM with local road vector data for transportation-network extraction.

Cross-zone Data Merging And Processing

• Scenario: Provincial or regional data may cross multiple UTM zones.
• Usage: Select a cross-zone projection or custom projection to merge the data into one consistent coordinate system.
• Example: Merge DEM data spanning two UTM zones into a continuous elevation model.

Historical And Modern Data Comparison

• Scenario: Historical maps may use deprecated local coordinate systems, such as Beijing 1954.
• Usage: Use coordinate transformation methods, such as three-parameter or seven-parameter transformations, to convert historical data to a modern coordinate system such as CGCS2000.
• Example: Compare urban expansion between data from the 1980s in Beijing 1954 and current data in CGCS2000.

3D Scenario Analysis

• Scenario: 3D analysis, such as line-of-sight analysis or shadow simulation, should use a planar projected coordinate system instead of a geographic coordinate system.
• Usage: Project data to a local projection such as UTM before 3D analysis.
• Example: Use a projected coordinate system when simulating building shadows to keep distance and angle calculations accurate.

Parameters

Basic settings (required)

Parameter	Description	Data type
Input vector file	File to reproject.	Point, line, or polygon
Target spatial reference	Target coordinate system after transformation.	Coordinate reference system
Output path	Folder where the result file is saved.	Folder path
Output file name	Name of the output vector file.	Text without extension

Advanced settings (optional)

Parameter	Description
File format	Specifies the output file format. The default is GPKG VectorData (.gpv). Other supported formats include PostGIS VectorData (.pgv), ESRI Shapefile (.shp), Keyhole Markup Language (.kml), GeoJSON (.geojson), and AutoCAD DXF (.dxf).
Output specified fields	When enabled, you can manually configure output fields. When disabled, the original field structure is retained.
Reproject	When enabled, sets the spatial reference for the output file. Otherwise, the input feature coordinate system is used.

Steps

1. Start the tool: Open Geoprocessing Toolbox > Data Management Tools > Projection, then start Reproject Features.
2. Set basic parameters: In Basic settings, set the input vector file, target spatial reference, output path, and output file name. All basic parameters are required.
3. Set advanced parameters if needed: Configure output file format, selected output fields, or reprojection options.
4. Run and monitor the task: Click Run. You can view progress, runtime, and status in Task List.
5. Handle failures if needed: If the run fails, review the error message and use Edit to return to the tool pane.

Notes

Projection Transformation Versus Define Projection

• Projection transformation changes coordinate values by converting data to a new coordinate system.
• Define projection only fixes coordinate system metadata. Coordinate values do not change.
• Common error: Defining a projection for data that already has a correct coordinate system can make coordinates wrong. Use define projection only when metadata is missing or incorrect.

Choose Geographic Transformations Carefully

• When different datums are involved, such as WGS 84 to CGCS2000 or NAD27 to NAD83, choose an appropriate geographic transformation method, such as a three-parameter or seven-parameter transformation.
• Ignoring the transformation method can cause offsets from 1 to 200 meters. Choose the method based on data location and accuracy requirements.

Consider Projection Distortion

• Projection transformation cannot remove distortion completely. Choose the projection based on the analysis purpose.
• Area analysis: Use an equal-area projection such as Albers.
• Shape preservation: Use a conformal projection such as UTM where appropriate.
• Distance measurement: Use an equidistant projection or a local projection suitable for the study area.
• For large areas, such as national or global datasets, select projections carefully to reduce distortion.

Elevation Data

• For data with Z values, confirm whether vertical datum transformation is required, such as EGM96 to a CGCS2000 vertical datum. Standard projection tools usually do not transform vertical datums automatically.