New Boundaries from Overlap
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David Orsi
Nov 13, 2015, 4:56:23 PM11/13/15
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I have a two part question:
Background: I have 2,400 DriveTime Polygons and I need to calculate where those DriveTimes overlap and create new boundaries based on those overlapping areas.
My questions are:
1. What is the best way to create new boundaries from the overlap of existing boundaries?
2. After creating the boundaries, is there a way to make the unique ID's of the original boundaries carry over into the newly created boundaries from the overlap? In other words is Store 1 and Store 5 have overlap and I create the new boundary from that overlap, can I make the newly formed boundary reflect the ID's from Store 1 and Store 5?
Thank you very much!
Background: I have 2,400 DriveTime Polygons and I need to calculate where those DriveTimes overlap and create new boundaries based on those overlapping areas.
My questions are:
1. What is the best way to create new boundaries from the overlap of existing boundaries?
2. After creating the boundaries, is there a way to make the unique ID's of the original boundaries carry over into the newly created boundaries from the overlap? In other words is Store 1 and Store 5 have overlap and I create the new boundary from that overlap, can I make the newly formed boundary reflect the ID's from Store 1 and Store 5?
Thank you very much!
Tony Pilkington
Nov 14, 2015, 2:20:59 AM11/14/15
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David, this mbx was designed to break a collection of polygons into unique
common linework segments with IDs of the 2 adjoining polygons as fields in the
output table (linework.tab). As a test case I include an old table of Africa to
decompose. An output value of –1 indicates no neighbour; sea?
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Andrew Harfoot
Nov 16, 2015, 6:58:11 AM11/16/15
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Hi David,
The method you are looking for is usually known as a Union, but isn't implemented as a single operation in MapInfo (unless somebody tells me otherwise). Here are the steps you'd go through:
To create the overlap polygons, you should use the Enclose operator - create a new table with (as a suggestion) an OverlapID (integer), DTPolyIDs (character), OverlapCount (integer) attributes. Add the new table to the map, make it editable, select all the DT polys, and then run Object > Enclose. Untick the box saying 'Ignore region objects'.
You can then use a number of Table > Update Column commands to populate the attributes of your new table:
To generate a unique ID for the overlap polygons:
To Count the number of overlaps:
To generate a list of the DT polygons that overlap in each polygon:
I'm assuming that there may be more than two DT polygons overlapping within your dataset, which makes the extraction and recording of the original IDs more complex, requiring a select and then update:
SQL Select all the original DT polys that overlap each 'overlap' polygon:
Gather all the IDs together into a delimited list (With leading and trailing colons on the list eg: :1:23:561: to help with searching subsequently)
I hope that helps,
Andy
The method you are looking for is usually known as a Union, but isn't implemented as a single operation in MapInfo (unless somebody tells me otherwise). Here are the steps you'd go through:
To create the overlap polygons, you should use the Enclose operator - create a new table with (as a suggestion) an OverlapID (integer), DTPolyIDs (character), OverlapCount (integer) attributes. Add the new table to the map, make it editable, select all the DT polys, and then run Object > Enclose. Untick the box saying 'Ignore region objects'.
You can then use a number of Table > Update Column commands to populate the attributes of your new table:
To generate a unique ID for the overlap polygons:
Update Table: OverlapPolys
Column to Update: OverlapID
Expression: rowid
To Count the number of overlaps:
Update Table: OverlapPolys Column to Update: OverlapCount
Get value from table: DT_polygons (the original table)
Join: Where objects from table OverlapPolys are within objects from DT_polygons
Calculate: Count
To generate a list of the DT polygons that overlap in each polygon:
I'm assuming that there may be more than two DT polygons overlapping within your dataset, which makes the extraction and recording of the original IDs more complex, requiring a select and then update:
SQL Select all the original DT polys that overlap each 'overlap' polygon:
Select Columns: OverlapPolys.DTPolyIDs, DT_polygons.ID
From Tables: OverlapPolys, DT_polygons
Where: OverlapPolys.Obj Within DT_polygons.Obj
Order by: DT_polygons.ID
Into: q_OverlapToUpdate
Gather all the IDs together into a delimited list (With leading and trailing colons on the list eg: :1:23:561: to help with searching subsequently)
Update Table: q_OverlapToUpdate Column to Update: DTPolyIDs Calculate: ":"
Update Table: q_OverlapToUpdate Column to Update: DTPolyIDs
Calculate: DTPolyIDs + ID + ":"
I hope that helps,
Andy
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-- Andy Harfoot GeoData Institute University of Southampton Southampton SO17 1BJ Tel: +44 (0)23 8059 2719 Fax: +44 (0)23 8059 2849 www.geodata.soton.ac.uk
Andrew Harfoot
Nov 16, 2015, 7:29:21 AM11/16/15
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Note that if you were only interested
in the overlapping areas, then you could select all the polygons
from OverlapPolys where OverlapCount < 2 and delete them.
Andy
Andy
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