NRSC 2230 / GEOG 2750

Useful Mapping Functions

General Pointers

Some frequently occurring points to be careful of are:

  1. Need to adjust the scalebar units to metres / kilometres
  2. Need to adjust the scalebar divisions to generally acceptable sizes e.g. multiples of five (0,5,10 etc.)
  3. Need to make careful use of ‘white space’.  The entire page should not be totally filled, but there must not be too much empty space
  4. Need to make a final check on the mapscale being presented.  After making adjustments, the mapscale value sometimes changes and may be non-intuitive e.g. 1:423,200.  Before finalizing your map the scale should be something the reader can relate to.  In the example above, the scale should be changed to 1:400,000 or 1:425,000.

Symbolization – Using Attributes to create categories

This enables us to create a map in which we can represent different attribute values from the same field in the table using different symbols.

This short Youtube video illustrates the process.

Instructions:

  1. Right Click the layer name in the ArcMap Table of Contents
  2. Select ‘Properties….’
  3. Select the ‘Symbology’ tab
  4. Select ‘Categories’ in the Features window (on left)
  5. Use the drop down box to assign the ‘Value field’.
  6. Click the ‘Add All Values’ button
  7. Edit the symbols
  8. Edit the labels

Symbolization – Creating Label classes

This enables us to display different text properties when labeling feature categories.

 

 Instructions:

  1. Right Click the layer name in the ArcMap Table of Contents
  2. Select ‘Properties….’
  3. Select the ‘Labels’ tab
  4. Change the ‘Method’ to “Define classes of features and label each class differently
  5. Click the ‘Add’ button
  6. Provide a name in the dialog box
  7. Hit the ‘SQL Query’ button to define the features that comprise this class
  8. Assign the ‘Label Field’
  9. Assign the text symbol (font, colour, size, etc.)
  10. Repeat steps 5 – 9 for all other classes
  11. Turn off the ‘Default’ class
  12. Hit OK

Geo-referencing a scanned image

The process enables us to place the features represented on a scanned image, in their approximate geographic location.  The process is presented in five parts namely, prepare data, load data, define map area, perform an approximate geo-referencing, perform a detailed geo-referencing.

A. Prepare Data

  • Identify the relevant NTS sheet (refer to query tool in blog)
  • Create a folder with sub-folders for shapefiles and images (if necessary)
  • Download and extract the required digital files to the relevant folders
  • Rename the coded digital files
  • Identify and note the coordinates of at least four easily identifiable reference points on the scanned image (in our example we can find the latitude and longitude coordinates). These points should be well distributed across the image. Here we will choose four points in the NW, NE, SE and SW corners.
  • (In our case we will convert the coordinates from Degrees Minutes to Decimal degrees ie. Degrees + (Minutes / 60).

B. Load Data

  • Load the road, stream and waterbody shapefiles into ArcMap
  • Load the scanned image into ArcMap
  • Load the ‘Georeferencing’ toolbar (View -> Toolbars -> Georeferencing)

C. Define the map area

  • Launch the ‘Go To XY’ tool in ArcMap
  • Select the units as Decimal Degrees
  • Enter the longitude and latitude coordinates of the first reference point
  • Click the Add Point button on the Go To XY toolbar to add a reference point on the digital file
  • Repeat the process to add points for all other reference points
  • Use the Zoom tool to zoom in to the area defined by your reference points

D. Perform an approximate geo-referencing

Geo-referencing is accomplished by creating links between known points on the scanned map and the actual points on the digital file.  The process is always from point on the scanned map to the point on the digital file.

  • Ensure that the Layer in the geo-referencing tool refers to the scanned map
  • Click the Georeferencing tool and select Fit to Display
  • Use the Zoom Tool to zoom in to a reference point on the scanned map
  • Select the Add Control Point tool from the Georeferencing toolbar
  • Click on the point on the scanned map
  • Zoom out by right clicking on the river layer in the ArcMap Table of Contents (window on the left)
  • Zoom in on the related point created by the Go To XY tool
  • Select the Add Control Point tool from the Georeferencing toolbar
  • Click on that point to establish a link between the scanned map and the digital file.
  • Repeat the process so that you link all scanned reference points to the reference points on the digital file
  • Click the View Link Table on the Georeferencing toolbar
  • Look at the values in the Residual column in the table and the Total RMS Error value at the bottom of the table.  The value in the residual column tells us how good the match is between the point on the scanned map and the point on the ground.  The Total RMS Error tells us how all the points fit as a group.  In either case, the smaller the value the better the fit.

E. Perform a more accurate geo-referencing

In this case the features on the scanned map will be linked to the features on the digital file e.g. stream.  Again the features used to make these links should be well distributed.

  • Use the Zoom Tool to zoom in to an identified river junction
  • Create a link between the location on the scanned map and the same location on the stream digital file.
  • Zoom in and out in order to create several links between the scanned map and the digital file
  • Open the Link Table
  • Review the values in the Residual column
  • If there are any values that are really large in comparison with the others, you may select the row and delete it (delete button on right of table)
  • Experiment with adding links to try to reduce the Total RMS Error
  • To finish, click the georeferencing tool and select Update Georeferencing.