Dear Devdatta and Nikhil, I attended a R GIS school where the teachers were from France and they were using CRS 2154. They told us that they were not familiar with the CRS for Indian maps.
I used 2154 thinking that it would not make much of a difference, but I was wrong. My apologies for the confusion. When I used that on Indian ( datameet ) shapefiles,I got this : map1.png ( see attachment ) I have also attached the R code to create these maps from the Datameet District level ( 2011 ) shapefiles. I have created map2.png and map3.png from crs = 3857 / 7755 respectively. I also found this : https://epsg.io/?q=india Which is confusing because many CRS are there for India. Why do we have so many choices of CRS for India ? I guess for the time being I will use 7755. Many thanks to Devdatta and Nikhil for their help. Best Regards, Ashim On Tue, Apr 16, 2019 at 11:42 AM Nikhil VJ <[email protected]> wrote: > Hi Ashim, > > Pls provide the exact link of what you're referring - this stuff is never > as much on the top of people's minds as we assume it to be. > Do try loading your shapefiles on other tools and check there : > mapshaper.org is a site that does a lot of quick, cool things with > shapefiles; QGIS is a software that does everything with shapefiles. Both > are free and open source. > > The latter will help you re-save the shapefile into any CRS you want. > Right-click the layer > Save As (or "Export") and remember to choose your > preferred CRS in the dropdown. > > Can you give background on what this CRS : *2154* : is and why you want > to transform to that? Because I've only come across two main CRS's both > being under the "WSG 84" category : > - EPSG 4326 : this makes everything in latitude longitude > - EPSG 3857 : this makes everything in meters from the equator (I think) > and we need to get the data in this format when we want to do things in > physical distance terms like making a 1km distance buffer or measuring areas > > I haven't learned GIS stuff from theory, I just use it, so don't know more > details about CRS. I do understand that the dizzying multitude of CRS's out > there are so because apparently GIS folks like to re-orient the center of > the world (geometrically speaking) to where their data is to ensure least > distortion of their shapes in the rendering. When I come across anything > that's in a non-standard CRS, my first move is to transform it to either > lat-longs (4326) or meters (3857). > > Regards > Nikhil VJ > > > On Monday, April 15, 2019 at 1:57:20 PM UTC+5:30, Ashim wrote: >> >> Dear All, >> >> I am referring to 2011_Dist. * set of shapefile. (District level >> shapefiles). >> >> When I read them as simple features in R, ( like this ) >> >> map <- st_read("2011_Dist.shp") %>% st_as_sf() >> >> ( it's unprojected because it says 4326 in the epsg when I read the above >> ) >> >> plot(map$geometry) >> >> it looks OK. >> >> But when I do : >> >> map <- st_read("2011_Dist.shp") %>% st_as_sf() %>% st_transform(crs= 2154) >> >> plot(map$geometry) >> >> the map is TILTED. >> >> What is the correct projection to use for this dataset? Please clarify. >> >> Best Regards, >> Ashim >> > -- > Datameet is a community of Data Science enthusiasts in India. Know more > about us by visiting http://datameet.org > --- > You received this message because you are subscribed to the Google Groups > "datameet" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- Datameet is a community of Data Science enthusiasts in India. Know more about us by visiting http://datameet.org --- You received this message because you are subscribed to the Google Groups "datameet" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
map.R
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