How do I view point coordinates in Cartographica?

Cartographica provides a number of different ways to show coordinates for features.   In the case of points, there are three primary ones, each with their own advantages.

Point Data Window

The Point Data window is accessible from the Windows menu and shows all parts and points for the selected geometry.   It is useful for all feature types (points, polygons, and lines) and shows the coordinates in the coordinate system of the layer itself, as opposed to the coordinate system of the map being viewed.

The Point Data window is a read/write window, so you can add/delete/edit points by modifying the coordinates in this window.   Changes take effect immediately and are undoable.

Add Coordinates Columns

Add Coordinates Columns adds 2 columns, one each for X and Y coordinates of the features in the layer.    This command adds this data to the layer and will be saved as a modification when the map set is closed (assuming you don't cancel the save).    When used, the Add Coordinates Columns command adds two new columns and sets the column data based on the current Map coordinate system.  As such, it can be an easy way to add coordinate columns for multiple coordinate systems.   For example, if you have feature data in UTM and want to have both UTM and Latitude/Longitude coordinates in your data area, you can do so through the following steps:

  1. Choose Tools > Add Coordinate Columns
    This will add new columns named X and Y to the data area.   These columns will contain the UTM data.
  2. Open the Layer Info window (choose Windows > Show Layer Info if it isn't visible)
  3. Change the name of the X and Y columns so that they won't conflict with the new columns.    For example: UTM X and UTM Y
  4. With the Map window foremost, choose Map > Project Map… and select WGS 84 coordinate system (latitude and longitude in WGS 84)
    The displayed map will likely shift a bit
  5. Choose Tools > Add Coordinate Columns again
    This will add new columns named X and Y to the data area.   These columns will contain latitude, longitude data. 
  6. Optionally rename the coordinate columns and restore the previous coordinate system
These columns are not live and will not change if new points are added or new coordinates are changed in the data by moving a point.

Formula Columns for X and Y

The last method is a blend of the two previous methods.   It provides dynamic columns that display data based on the current Map CRS which change when the CRS is changed or when the data points themselves change.   It's a bit trickier to set up.

  1. Open the Layer Info window (choose Windows > Show Layer Info if it isn't visible)
  2. Add a new column using the + button
  3. Change the column name as appropriate
  4. Change the data type to Float by selecting from the menu
  5. Click Set Formula… to bring up the formula setting window
  6. Now enter geometry.centroid().x in the box and click OK
  7. Repeat steps 3-6 for the Y column, using geometry.centroid().y as the formula
    At this point, you should have 2 new columns, one each with the X and Y coordinates for the existing features

Bonus hint: if you use geometry.centroid(1).x and geometry.centroid(1).y the original coordinates of the layer will be used instead of the projected coordinates.

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    Les van Rooyen


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