On-The-Fly-Projection in ArcGIS Pro
On-the-fly projection in ArcGIS Pro allows you to visualize and work with layers that have different coordinate systems without permanently transforming the data. This feature is powerful but requires careful handling to ensure accurate spatial analysis and display.
1. Understanding On-the-Fly Projection
- Dynamique Projection allows different datasets with varying coordinate systems to be displayed together seamlessly.
- Dynamic Transformation: ArcGIS Pro dynamically reprojects data from its native coordinate system to the coordinate system of the map or scene. This is done in real-time and does not alter the original data.
- Display Consistency: It allows you to display layers with different coordinate systems together, ensuring that they align correctly on the map.
- Analysis: for accurate analysis, it's often better to reproject datasets to a common coordinate system.
The map below depicts the locations of indigenous communities in coastal areas across the U.S.A and territories that may face or are already experiencing the effect of Sea Level Rise (SLR).
The Indigenous communities' layer has a projected coordinate system (PCS): WGS 1984 Web Mercator (auxiliary sphere).
The Climate Indicator Sea Level Change 1880-2021 (EPA 2022)' layer has a geographic coordinate system (GCS): NAD 1983.
In the example above the datasets not only use different coordinate systems, but they are also based on different datums. However, ArcGIS Pro can display them correctly in their respective locations by dynamically reprojecting the data on-the-fly.
2. Setting the Map Coordinate System
- Map Properties: Set the coordinate system of your map or scene to the most suitable projection for your analysis or display needs. Right-click on the map in the Contents pane, select Properties, and go to the Coordinate Systems tab.
- Consistent Basemap: Use a basemap that matches or is compatible with the coordinate system of your project to avoid unnecessary transformations.
3. Verify Layer Coordinate Systems
- Layer Properties: Check the coordinate system of each layer by right clicking the layer, selecting Properties, and viewing the Source tab. This helps identify any layers that might need on-the-fly projection.
- Consistent Data: Ensure that all layers are correctly defined. If a layer’s coordinate system is undefined or incorrect, use the Define Projection tool to set it.
4. Performance Considerations
- Large Datasets: On-the-fly projection can affect performance, especially with large datasets or complex geometries. Consider projecting large datasets to the map’s coordinate system using the Project tool for better performance.
- Simplify Layers: Simplify or generalize layers where possible to reduce the computational load during on-the-fly projection.
5. Geographic Transformations
- Transformation Prompts: When layers with different datums are added to a map, ArcGIS Pro may prompt you to select a geographic transformation. Choose the most appropriate transformation for your region and data accuracy requirements.
- Manage Transformations: Access and manage geographic transformations through the map’s properties to ensure they are applied correctly. Go to Map Properties > Coordinate Systems > Transformations.
6. Visual Verification
- Overlay with Basemaps: Add a basemap to your map to visually verify the alignment of your layers. This helps identify any misalignment issues that might be caused by incorrect projections.
- Measure Tools: Use measurement tools to check distances and areas to ensure they are reasonable and consistent with the real world.
7. Data Export and Sharing
- Projected Export: When exporting maps or data, ensure that the coordinate system of the output matches the intended use. Exporting with on-the-fly projection active may result in data that appears correctly but has underlying coordinate system mismatches.
- Metadata: Include coordinate system information in the metadata when sharing data to ensure recipients understand the spatial reference and any transformations applied.
8. Symbology and Labeling
- Consistent Symbology: Symbology may appear different when layers are reprojected on-the-fly. Verify that symbology settings are appropriate for the transformed data.
- Label Placement: Labels might shift due to on-the-fly projection. Adjust label placement settings to ensure labels are positioned correctly after projection.
9. Advanced Analysis
- Reproject for Analysis: For spatial analysis tasks such as overlay, proximity, or network analysis, it is often better to reproject the data to a common coordinate system using the Project tool. This ensures the accuracy and reliability of the analysis results.
- Coordinate System Compatibility: Ensure that the coordinate systems of all input datasets are compatible for analysis to avoid projection-related errors.
By following these tips and tricks, you can effectively manage and utilize on-the-fly projection in ArcGIS Pro, ensuring accurate and efficient spatial data visualization and analysis.
We hope that this article has been helpful! If you have any feedback or questions, please feel free to send us an email or connect with us for a chat. The NTGISC team is here to assist you further!