For my project at work, I am trying to compare and contrast property information with points I have mapped (from my workplace)

Example: I have points with information on water samples, the results of their chemical testing, well depth and date sampled.

I have tax parcel polygons for each county (U.S.) and that table can tell me whether that property has a private or public well

I'm interested in finding what points are on properties that have a private or public well, or no well.

I was thinking of trying to make a thematic map for each, but it gets confusing fast. I was thinking of applying X color for private wells, Y color for public supply, and Z for none or other. After that, I was going to apply a range of low to high levels of toxicity for the chemical our workplace is investigating, that has 4 different colors.

Is there a less complicated way of comparing/contrasting polygon information with point information in two separate tables that can't be joined?

I am new to MapInfo, and have not had an easy time finding guidance on how to interact with the software. This is my first GIS software program that I've jumped into using, with just a few hours of training and a lot of trial and error.

  • 1
    Why can't the tables be joined? Sounds like a spatial join is possible. – lynxlynxlynx Jul 16 '18 at 18:40
  • Added more details to the question- in short, I am not sure how to do that or if it's possible with the two tables. – ElizB Jul 16 '18 at 18:50

If you want to try a table join, use the Spatial Join tool. Make your water sample file the target and join it with the polygon. Wherever a point and polygon overlap (intersect), it will pull the details from the polygon and add them to the attribute table of the water sample file. You could also try reversing it and making the polygon the target file too. The results make a new file so you do not corrupt your original data.

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I'd suggest inspecting the spatial join option.

Your query could look like this:

Select Parcel.ID
     , WaterSample.ID, WaterSample.Toxicity, WaterSample.Date, WaterSample.Depth
   From WaterSample, Parcel
   Where WaterSample.OBj Within Parcel.OBJ
   And Parcel.WaterSupply = "Private Well"
   And WaterSample.Toxicity > 100

In the statement above, you join the two tables where the sample points are within the parcel boundary/polygon. Then you add the condition to only select the record where the Water Supply is via a Private Well and where the Toxicity level is above 100.

You can of course change these criterias to values that match your requirements. If you want to include both private and public wells, change that condition to:

   And Parcel.WaterSupply In ("Private Well", "Public Well")
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