on December 29, 2022

Calculating X and Y of line start and line end using ArcPy?

Hiking & Activities

Getting Line Start and End Coordinates with ArcPy: A Human’s Guide

Ever needed to pinpoint exactly where a line starts and stops on a map? In the GIS world, knowing those coordinates is super useful. Think spatial analysis, tracing networks, or even just making a map look its best. ArcPy, Esri’s Python toolbox for ArcGIS, comes to the rescue! It lets you dive into a map’s DNA and grab the X and Y coordinates of any line’s endpoints. Let’s break down how to do it, no PhD required.

Cracking the Geometry Code

Imagine each line on a map has a secret code – that’s its geometry. This code tells you its shape and location. For lines, the geometry is like a connect-the-dots game, with each dot being a vertex. ArcPy lets you access these dots, and the first and last ones? Those are your start and end points!

Two Paths to the Same Destination

There are basically two ways to snag those coordinates using ArcPy. The first is like using a ready-made gadget, super simple. The second? It’s more like building your own tool, giving you total control.

  • The “Calculate Geometry Attributes” Shortcut: ArcGIS Pro 2.2 and later versions have this awesome tool called “Calculate Geometry Attributes.” It’s like a magic wand that populates your attribute table with the start and end coordinates. Seriously, it’s almost too easy.
  • ArcPy and the Search Cursor: The DIY Approach: This involves writing a little Python script with ArcPy. You use a “search cursor” to walk through each line, grab its geometry, and pluck out the coordinates of the first and last points. It’s a bit more involved, but you’re the boss here!

    • Let’s Get Practical: Using “Calculate Geometry Attributes”

    Okay, let’s say you have a map of hiking trails and you want to know the exact coordinates where each trail begins and ends. Here’s how you’d do it with the “Calculate Geometry Attributes” tool:

  • Peek at the Attribute Table: In ArcGIS Pro, open the table that holds all the info about your trails.
  • Make Room for the Coordinates: Add four new columns to the table: start_x, start_y, end_x, and end_y. Make sure they’re set to “Double” so they can hold decimal numbers.
  • Time to Calculate! Right-click on the start_x column and choose “Calculate Geometry.”
  • Tell the Tool What to Do:
    • The tool should automatically know which map layer you’re working with.
    • For the “Field,” pick start_x.
    • Under “Property,” select “Line Start X-Coordinate.” This tells the tool to grab the starting X coordinate of each line.
    • Double-check that the “Coordinate System” is correct for your map.
  • Hit “OK” and Watch the Magic Happen! The start_x column will now be filled with the X coordinates of each trail’s starting point.
  • Rinse and Repeat: Do the same for start_y (using “Line Start Y-Coordinate”), end_x (“Line End X-Coordinate”), and end_y (“Line End Y-Coordinate”).

    • Getting Down and Dirty: ArcPy with Search Cursors

    Want more control? Let’s write some code!

  • Summon ArcPy: Start your Python script with import arcpy.
  • Point to Your Map: Tell ArcPy where your map layer is located on your computer.
  • Unleash the Search Cursor: This is the key! The search cursor lets you go through each feature (each line) in your map layer.
  • Grab the Geometry: Inside the loop, you’ll grab the “SHAPE@” which holds the geometry of the line. Then, .firstPoint and .lastPoint give you the start and end points.
  • Extract the Goods: Use .X and .Y to get the actual coordinates from those points.
  • Do Something with the Coordinates: Print them, save them to a list, whatever you need!
  • Update the Map (Optional): If you want, you can add the coordinates as new columns in your map layer’s attribute table.

    • Here’s that code snippet again, tweaked for clarity:

    python

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