on December 30, 2022

How to calculate length of feature in MapInfo

Hiking & Activities

Figuring Out Feature Length in MapInfo: A Plain-English Guide

Okay, GIS folks and mapping buffs, let’s talk about something fundamental: measuring the length of stuff in MapInfo. Whether it’s a tiny line or a whole bunch of features, getting accurate lengths is key. MapInfo Pro gives you a few ways to do this, so you can be sure your measurements are spot-on. Let’s dive in!

First things first, you gotta know the basic tools MapInfo offers for length calculations. The big one is ObjectLen(), which calculates the length of, well, an object. But here’s the catch: ObjectLen() isn’t a one-size-fits-all deal. There are variations, and picking the right one depends on your coordinate system. Think of it like choosing the right wrench for the job.

  • ObjectLen(): This is your general-purpose function. Got data in Latitude/Longitude? This bad boy calculates the spherical length, meaning it takes the Earth’s curve into account. Pretty neat, huh?
  • CartesianObjectLen(): Now, if your data is projected – meaning it isn’t using a Lat/Long coordinate system – you’ll want CartesianObjectLen(). This calculates length on a flat, Cartesian plane. Trust me, using ObjectLen() on projected data is a recipe for inaccurate results. I learned that the hard way once, spending hours troubleshooting a seemingly simple calculation!
  • SphericalObjectLen(): As the name suggests, this function explicitly calculates lengths considering the Earth’s curvature.

Seriously, choosing the right function is crucial. Using CartesianObjectLen() for long distances on geographic coordinate systems? You’re gonna have a bad time. It’ll ignore the Earth’s curve, and your numbers will be way off.

Method 1: The Update Column Trick

This is a slick way to add length measurements right into your data’s attributes. I use this all the time.

  • New Column Time: Open your table and head to TABLE > Table > Modify Structure. Add a fresh column – call it “Length,” or whatever floats your boat – and set the data type to Float.
  • Update Magic: Now, go to TABLE > Update Column. In the dialog box:
    • Make sure your table is selected in both “Table to Update” and “Table to get value from.”
    • Pick your shiny new “Length” column as the one to update.
    • Hit that “Assist” button to bring up the Function List.
    • Choose either SphericalObjectLen or CartesianObjectLen (remember what we talked about earlier!) and tell it what units you want (km, mi, m, ft – you name it).
    • Click “OK” to close the dialogs and let MapInfo work its magic.

    • Boom! Your table now has a “Length” column filled with the length of each feature. Pretty sweet, right?

    Method 2: SQL Select for Total Length

    Need to calculate the sum of lengths for a bunch of selected lines? This method’s your friend.

  • Select Your Lines: Pick the line segments you want to measure. Click one, hold Shift, and click the rest. Or, if you’re feeling fancy, use a query to select them based on their attributes.
  • SQL Time: In 64-bit MapInfo Pro, go to Spatial > Selection > SQL Select.
  • Enter the Secret Code: In the SQL Select dialog box, type in this query:
    sql

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