Creating Point Themes

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Creating Point Themes
John Q. Murray Murray Information Services, Inc.
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Two ways to add points

• Draw points on the map right where you want them
• Add point data from a file
• Note You may sometimes need to project the point
  data to match other themes coordinate systems

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Method 1 Draw on the map

• Open a project
• From the View menu, select New Theme
• In the New Theme dialog, you can choose point,
  line, or polygon feature types Choose Point
• Pick a filename to save the points Enter
  mypoints.shp

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Draw points on the map

• The themes checkbox shows that you are editing
• Select the Draw Point button from the toolbar
• Note The buttons are on dropdown menus click
  the lower right corner to see them all
• Click on the map where you want to add the point

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Save your point theme

• Save the theme From the Theme menu, select the
  Save Edits command
• Stop Editing From the Theme menu, select Stop
  Editing
• The theme changes back to show we are not editing

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Method 2 Add points from a file

• The file mypoints.txt is a text file that
  defines two points using their x,y values
• Add the file as a table
• From the Project, select Tables, then click Add

• In the Add Table dialog under List Files of
  Type choose Delimited text
• Select the file mypoints.txt

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Add the table as an event theme

• Return to View1
• From the View menu, select Add event theme

In the Add Event Theme dialog As Table
select mypoints.txt As X field select
X-coord As Y field select Y-coord Click OK
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Method 2 with a twist

• Add points from a file when the points are in a
  different coordinate system
• Add the latitude/longitude points in the file
  mylatlon.txt
• Like the previous example but 2 new steps
• Convert to a shapefile
• Use the Projection Utility

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Add lat/lon points from a file

• The file mylatlon.txt is a text file that
  defines two points using their latitude,
  longitude values
• Add the file as a table
• From the Project, select Tables, then click Add

• In the Add Table dialog under List Files of
  Type choose Delimited text
• Select the file mylatlon.txt

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Add the table as an event theme

• Return to View1
• From the View menu, select Add event theme

In the Add Event Theme dialog As Table select
mylatlon.txt As X field select
Longitude As Y field select Latitude Click
OK
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They arent in the right spot

• These points are in a different coordinate system
  and need to be projected
• Make sure the Projection Utility is active

• From the File menu, select Extensions
• In the Extensions dialog, check Projection
  Utility Wizard
• Click OK

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Convert the theme to a shapefile

• In View1, make sure mylatlon.txt is highlighted
• From the Theme menu, select Convert to Shapefile

• Save the theme as the shapefile mylatlon.shp
• Click OK

When prompted, Add shapefile as theme to the
view?, click Yes
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Project the theme

• From the File menu, select ArcView Projection
  Utility

The ArcView Projection Utility displays a splash
screen Verify that mylatlon.shp is selected,
then click Next
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Set the current coordinate system

• In Step 2, for Coordinate System Type, select
  Geographic
• For Name, select GCS North American 1983
• For units, select Degree
• When prompted to save this coordinate system
  information, choose either Yes or No (it
  doesnt matter for this task)

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Set the new coordinate system

• In Step 3, for Coordinate System Type, select
  Projected
• For Name, select NAD83_Montana
• For units, select Feet
• Select Next
• Select the Browse button to enter a filename

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Confirm the projection

• In the Save As dialog, enter the filename
  projlatlon.shp
• Click Save
• Click Next to see the Summary screen
• Click Finish

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View the projected shapefile

• When the projection utility is complete, click
  OK
• When you are asked, Do you want to add your
  projected data? click Yes
• In the Add projected data dialog, select the
  file you just created projlatlon.shp

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View the projected point data

• Add the projected lat/lon point data to View1
• Click OK
• Select the new theme Projlatlon.shp so that it
  is visible
• Verify that the points appear in the correct
  location