View - Graticule

The View - Graticule command displays or creates a grid of lines that are parallel to meridians of longitude and parallels of latitude. Graticule lines will be curved in geographic projections.

 

Graticules may be shown as system items in the window or may be saved as objects into a drawing. Graticules may also be used with Snap to precisely locate map clicks.

 

Show Graticule

Check box to show graticule.

From / To

The beginning and end Longitude and Latitude values the graticule should span.

Spacing

Longitude and Latitude spacing of graticule lines.

(Units box)

Not enabled for graticules, which always use degrees.

Same Spacing

Check so that any change in Longitude spacing will update Latitude spacing as well and vice versa. Use if the same Longitude and Latitude graticule spacing is desired.

Segments

The number of coordinates to use per graticule line. More segments will allow for smoother curves if lines created with graticules are projected.

Style

Graphics style used to show graticule.

Size

Width of line in printer's points to use for the graticule line.

Suggest

Load suggested defaults for the current view.

Create

Create actual line objects in the drawing for the grid. Use carefully, since every press of the Create button will create another set of lines.

 

Most "whole world" graticules are laid out from -180 to 180 degrees Longitude and from -70 to 70 degrees Latitude in spacing of 10 degrees. This provides a pleasing effect when used with maps of the entire Earth.

 

If a very large number of graticule cells (greater than 10000) would be created given the specified settings, Manifold will ask for a confirmation in case of error.

 

Creating Graticules as Objects

 

The graticule that appears when the Show Graticule box is checked is not part of any layer. It is something created by the system and overlaid upon the map window. It does not really exist and cannot be selected or otherwise manipulated. The default graticule color is set by an option in Tools - Options .

 

We frequently will want to create actual objects, lines, in the form of the graticule to allow us to better manipulate the graticule in graphics arts effects. For example, we might wish to position the graticule in a drawing layer in a map so that it is above some layers (oceans objects) and below others (continents). Alternately, we might want to select some of the lines that make up the graticule and delete them so we have a graticule in some places but not in others. This is of interest sometimes to create a proper appearance when using "interrupted" projections.

 

To create line objects, set up the graticule as desired in the View - Graticule dialog and then press the Create button. The graticule will be created in the active drawing as line objects. These may then be manipulated like any other lines. In maps it is often convenient to first create a new blank drawing with a right click on a layer tab and using Add - New Drawing, to rename the new drawing "graticule" and to then create the graticule in that layer.

 

Example

 

images\sc_graticule_01.gif

 

If we create a graticule on a world map (seen in Latitude / Longitude projection) it will overlay all objects in the map. The graticule shown extends from -180 to 180 degrees longitude and from -70 to 70 degrees latitude using a spacing of 10 degrees.

 

We can use Add - New Drawing to create a new drawing and then create a graticule by pressing the Create button in the View - Graticule dialog.

 

images\sc_graticule_02.gif

 

To see the new set of graticule lines, we uncheck the Show Graticule box in the dialog (otherwise, the graticule shown by the system will precisely overlay and thus hide the new graticule just created). We can move the new drawing to a layer below the world map drawing and change the color of the lines in the graticule.

 

The Difference between Graticules and Grids

 

Graticules are always expressed in geographic coordinates (latitude and longitude) while grids are expressed in the native X and Y coordinates of the coordinate system of the component. For components using the Latitude / Longitude "non-projection", both graticules and grids will appear as a grid of horizontal and vertical straight lines.

 

In projected coordinate systems, graticules will be created as curved lines (if necessary) to parallel the curved form of meridians of longitude or parallels of latitude in the projection. Grids, however, will always appear as a grid of horizontal and vertical straight lines.

 

images\sc_graticule_and_grid.gif

 

In the image above a drawing of a world map is shown in Robinson projection with a graticule in magenta and a grid in blue. Note that the graticule has curved meridians while the grid uses straight lines only.

 

Tech Tip

 

Interrupted projections are not continuous coordinate systems. They employ multiple conversion domains with blank space between the different lobes of the conversion domains, as seen in the illustration below of the Mollweide Interrupted projection.

 

images\sc_projections_mollweide_int.gif

 

It is absolutely essential to check the Clip Coordinates box in the Projection dialog whenever using such projections. This box causes Manifold to clip each object so that it exists only within the allowed conversion domain lobes and does not extend or cross through disallowed blank space. This is a highly computationally intensive process so the Clip Coordinates box is not checked by default, so that significant overhead is not imposed if it is unnecessary.

 

Dealing with the separate conversion domain lobes of an interrupted projection requires a manual approach to creating graticules, since the graticule lines normally extend through the blank space between lobes. Use the following procedure:

 

1. Create a latitude / longitude drawing.

2. Use the View - Graticule tool to create the desired graticule, using the option to Create the graticule as line objects.

3. Project the drawing into the desired interrupted projection, making sure to check Clip Coordinates.

4. Edit the graticule lines by selecting undesired lines and deleting them, or by adding lines.

 

For many uses the fastest method is to add lines. Let's consider an example of creating a graticule for use with Mollweide Interrupted. Suppose we begin with a latitude / longitude drawing in which a graticule was created with lines every 10 degrees from -180 to 180 longitude and from -70 to 70 latitude.

 

images\sc_graticule_int_01.gif

 

After projection into Mollweide Interrupted with Clip Coordinates checked, the lines that appear on the edges of the conversion domain lobes will have been deleted.

 

images\sc_graticule_int_02.gif

 

images\btn_snapto_lines.gif images\btn_shp_line.gif We can add lines by clicking Snap To Lines and then using the Insert Line tool to add lines between the "dangling" parallels. This goes very rapidly with less than a minute required to complete the graticule.

 

images\sc_graticule_int_03.gif

 

The result will be a graticule grid with lines restored that were deleted by Clip Coordinates. This procedure was used to create the graticule seen in the interrupted projection illustration above.