Guidance on digitizing boundaries

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Gufran Pathan

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Dec 26, 2020, 8:38:05 PM12/26/20
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Hi team,

I am trying to digitize ward boundaries for the city of Akola (Maharashtra) - create shape files so that I can visualize them along with associated data. I'm reaching out to get some guidance on how one would go about doing this? What does the process look like at a high-level? Does one get physical / PDF copies of the map with boundaries and then 'digitize' it? What tools are typically used in the digitization process? Is it largely a manual activity (does one need to manually draw the boundaries on a tool using the reference)?

I'd love any guidance and further readings that would help me with this.

Thanks,
Gufran

Digvijay Bendrikar Shinde

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Dec 26, 2020, 11:49:42 PM12/26/20
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A question on similar context, are the Ward wise boundaries of all municipal corporation available for use?

Where do we get them? 

If not shapefiles, where do we get latest ward wise maps?

Thank you in advance,
Regards
Digvijay

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vishal darji

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Dec 27, 2020, 12:41:00 AM12/27/20
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One can get ward boundary from respective  Corporation or municipality.
Very few corporations/municipalities have uploaded ward map on their website.

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Akshit Shah

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Dec 27, 2020, 5:56:39 AM12/27/20
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Hi Gufran and Digvijay,

You can get the pdf copy of maps from the following portal:

you can either import pdf in AutoCAD and separate the admin boundary layers > georeference them > and convert them to shapefile. your digitisation effort will be saved if the pdf has vector elements in it.

for Karnataka State there is a portal where you can find Admin boundary upto Town, wards and village level:  https://kgis.ksrsac.in/kgis/downloads.aspx#

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Warm Regards,
                                                                        
Ar. Akshit Shah
Associate - Research Service, Cushman & Wakefield India
M.Tech (Infra), IIT KGP | B.Arch, VNIT Nagpur

Digvijay Bendrikar Shinde

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Dec 28, 2020, 12:00:08 AM12/28/20
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Thanks Ar Akshit,

MRSAC don't have corporation ward wise boundaries PDF, they have revenue village and outer boundaries of towns and cities... But within the cities details are Missing.

Thanks about Karnataka link, will check.

Regards
Digvijay
(PhD scholar at CTARA, IIT Bombay)

Nikhil VJ

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Dec 28, 2020, 1:54:16 AM12/28/20
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Hi Gufran,

I had done georeferencing in QGIS of Pune's latest (2017) ward maps when they were published:

It's been used by lot of folks since then as I guess official digital shapefiles were never published though internally the corporation does seem to be using their own. There is an obvious disclaimer that it was manually done by volunteer and I've included the original maps and links for referencing - use at own risk, no guarantees. Corrections in case anything is wrong are most welcome.

I've found three ways to do the first crucial step of geo-referencing the pdf / image map:

There is one traditional way there which involves more work, but has lot more options like if your pdf/image is relatively distorted in proportions compared to actual map then you can do things to rectify. Sharing its link:
This involves clicking and marking common points between your image/pdf map and the actual map.

There is another quicker plugin in QGIS I had found later, which uses a different and much quicker approach, but works well only if your pdf/jpg is already good in proportions and doesn't have too much distortion.
This involves "floating" the pdf/image over the map and resizing, rotating it till it fits properly.

Then, there is a website called mapwarper that uses the the same approach as first solution but more streamlined (albeit with fewer power options):
Once the "warping" onto map is done, you can download the georeferenced TIF and load it on QGIS. Or you can publish your map, copy the tile layer string from the export section and import in QGIS as a XYZ tiles map layer.

Once the georeferencing is complete, you have a image layer properly fixed to lat-long map, which moves and zooms with the map. Now you can create an empty polygons shapefile and start manually tracing the boundaries. 

Tips from digitizing experience:
1. It's good to use Snap settings to make your boundaries snap to each other properly so you don't leave out slivers of no-mans-land or overlaps between wards. I found 20 pixels snap to be good.
2. These ward boundaries oftentimes follow along canals and roads. So, you can add a map satellite view background layer and keep it semi-transparent to assist you. 
3. Bring in any other boundaries file (like district etc) which might help you start from the outside.
4. If using the common points method, try to have a good spread of points. Avoid keeping any 3 consecutive points in a line, as small errors can get magnified. Crossroads/chowks are good places to pin.

Some links and video online that can guide through this process:

All the best, and do share when done - it'll be good to see more ward boundaries come up from MH!

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Cheers,
Nikhil VJ
https://nikhilvj.co.in


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Naveen Francis

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Dec 28, 2020, 9:05:10 PM12/28/20
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Hello Digvijay, 

Ward boundaries currently available in OSM - http://overpass-turbo.eu/s/11FQ  (this may change later; new tagging scheme is under discussion)


Thanks
naveenpf 

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