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In ArcGIS Desktop, the geographic coordinate system of a data frame or map can be different from the native geographic coordinate system of the data sources. When displaying multiple datasets with different geographic coordinate systems, you need a geographic transformation. Geographic transformations translate coordinates from one geographic coordinate system to another. ArcGIS Desktop will then project the data 'on-the-fly' to the coordinate system that is set for the data frame or map using the geographic transformation chosen.

When working with geographic transformations, if no mention is made of the direction, ArcGIS Desktop will handle the directionality automatically. For example, if converting data from WGS 1984 to NAD 1983 CSRS, you can pick a transformation called NAD_1983_CSRS_to_WGS_1984_1 and the software will apply it correctly.

Caution: If you need to edit or perform analysis on your data, it is good practice to work with data in the same coordinate system. Use the Project tool to project spatial data from one coordinate system to another. Please refer to the 'Reprojection of Data' Section for detailed instructions.

ArcMap

Steps to Project in ArcCatalog:

1. Open ArcMap

2. Add your first layer to the map, for example a CITYMTM layer (NAD 1983 CSRS MTM 10).

3. Right click on the active Data Frame 'Layers' < Properties < Coordinate System tab

4. Currently, the data frame coordinate system is defined as the first layer that was added to ArcMap, in this case, NAD_1983_CSRS_MTM_10.

5. You may add this projection to your favorites list for easier access in the future

6. Add your second layer to the map, for example, a layer from a web service. City's web services are published in WGS84 Web Mercator Auxiliary Sphere. ArcMap recognizes that there is a datum difference and displays A Geographic Coordinate System Warning.

7. Click the Transformations button

8. Choose Convert from 'GCS_WGS_1984' into 'GCS_North_American_1983_CSRS' using 'NAD_1983_CSRS_To_WGS_1984_1' and click OK.

9. Same transformation method can be used when converting from 'GCS_North_American_1983_CSRS' into 'GCS_WGS_1984' depends on which coordinate system the user choose to see their data in.

This process merely transforms the coordinates 'on-the-fly' without having to re-project the data. Failure to do so will result in an apparent shift when displaying both coordinate systems together.

ArcGIS Pro

Steps to Project on-the-fly in ArcGIS Pro:

1. Open ArcGIS Pro

2. Add a new map to your project, the map will start with the default Basemap (WGS84 Web Mercator Auxiliary Sphere)

3. Add your layer to the map, for example a CITYMTM layer (NAD 1983 CSRS MTM 10).

4. ArcGIS Pro recognizes that there is a datum difference and displays the Transformation Warning window from NAD 1983 CSRS MTM 10 to the datum of the Basemap (GCS WGS 1984)

5. In the GCS WGS 1984 Transformation drop down list, select 'NAD 1983 CSRS To WGS 1984 1' and click OK

6. Your features will now draw on the Basemap with no apparent shift

Same transformation method can be used when converting from 'GCS WGS 1984' into 'GCS North American 1983 CSRS' depends on which coordinate system the user choose to see their data in.

In ArcGIS Desktop, the geographic coordinate system of a data frame or map can be different from the native geographic coordinate system of the data sources. When displaying multiple datasets with different geographic coordinate systems, you need a geographic transformation. Geographic transformations translate coordinates from one geographic coordinate system to another. ArcGIS Desktop will then project the data 'on-the-fly' to the coordinate system that is set for the data frame or map using the geographic transformation chosen.

When working with geographic transformations, if no mention is made of the direction, ArcGIS Desktop will handle the directionality automatically.

Caution: If you need to edit or perform analysis on your data, it is good practice to work with data in the same coordinate system. Use the Project tool to project spatial data from one coordinate system to another. Please refer to the 'Reprojection of Data' Section for detailed instructions.

ArcMap

Steps to Project on-the-fly in Arc Map

Transformation method: Toronto NAD 1927 (1974) to NAD 1983 CSRS (1997) Version 1

Prerequisites: Install the custom geographic transformation file (.gtf) and transformation file (.gsb) to ArcGIS Desktop. Please refer to the 'Reprojection of Data' < 'ArcCatalog'/'ArcGIS Pro' 'Prerequisites' Section for detailed instructions.

Follow same steps as in the NAD83 CSRS to and from WGS84 section.

Steps to Project in ArcGIS Pro:

Follow same steps as in the NAD83 CSRS to and from WGS84 section.

The NAD27 MTM Zone 10 web services (e.g. cot_geospatial_mtm) will be decommissioned at the end of 2019. From that point forward web services will only be available in Web Mercator (EPSG: 3857).

Web Mercator is currently the standard for sharing data on the Web. By decommissioning the NAD27 MTM Zone 10 web services, we will ensure that our map data aligns properly with other services such as popular content providers Microsoft Bing Maps, Google Maps, and ESRI ArcGIS Online, which have standardized their services on the Web Mercator coordinate system.

If you have web applications that are using the NAD27 MTM Zone 10 web services or basemaps, please contact gcc@toronto.ca as early as possible for assistance.