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In order to display geometries correctly on a map, they must have coordinates. Often, the data available to the user is not in the coordinate system required for their project. In these cases the data needs to be projected to the desired coordinate system. There are two main types of coordinate systems used in GIS: Geographic coordinate systems: These use coordinates defined on an ellipsoid, so the units are usually degrees. For example: WGS1984 (EPSG:4326) Projected coordinate systems: These use coordinates on a flat, two-dimensional surface, with units such as meters. For example : EUREF-FIN TM35FIN ( EPSG: 3067) or Web Mercator Auxiliary Sphere (EPSG:3857). |
When do you need this?
When using data downloaded from Maptionnaire in a GIS software
Data exported from Maptionnaire is in the WGS84 geographic coordinate system (EPSG:4326). If your project uses a different coordinate system — for example, a national or regional projection — you need to project the data before using it.
When bringing your own data into Maptionnaire
If you want to publish your own map layers to Maptionnaire — for example, as a vector tile service — you must project them to Web Mercator (EPSG:3857) coordinate system. This ensures that your layers align correctly with the Maptionnaire map background.
Popular GIS software, like ArcGIS Pro, are containing these coordinate systems by default. The user just needs to select the correct one according to their needs.
In this article we are discussing the projection methods available in ArcGIS Pro.
On-the-fly projection
ArcGIS Pro includes an automatic feature called on-the-fly projection. It quietly "projects" layers in the background so they line up on the map, which can make it easy to overlook what coordinate system your layers are actually using.
When you create a new ArcGIS Pro project it is important to know that the map will use the coordinate system of the first layer added.
After this point any additional layers with differing coordinate systems are automatically projected to the map’s coordinate system in real time (“on-the-fly”). But this does not mean real projection!
The user can consider the on-the-fly projection as a display functionality, without altering the original data. Watch our video for more details:
Project
The data downloaded from the Maptionnaire website uses the WGS1984 coordinate system (EPSG:4326). This is a geographic coordinate system, and the units of the coordinates are degrees.
If the user wants to change the coordinate system of the data, they need to project it. In ArcGIS Pro, this can be done by using the Project tool.
- To open the tool, click on the Analysis ribbon and then click on the Tools button.
- In the Geoprocessing Pane search for the tool Project.
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Open the tool and set the parameters like Output file name and Output coordinate system.
If you are preparing your data to create an Esri Vector Tile Service, select the Web Mercator (EPSG:3857) coordinate system as Output Coordinate system.
When it’s all set, click on the Run button to start the Project tool. This will create a new file containing the data with the new coordinate system.
The new layer will be automatically added to the map.
Note: The user can always check the map’s current coordinate system by right clicking on the “Map” in the Contents pane and then selecting Properties, then select Coordinate Systems. If the very first layer added to the project used a different coordinate system, then the Current XY setting might still reflect that system, even after the output of the Project tool has been added to the Map.
To change the Current XY setting of the Map (not the layer!), click on the Map item in the Contents Pane, select Properties. Then, in the Coordinate System tab select the coordinate system required for the task and click OK.