Jump to content

 
Photo

Digitising - Advice and Tips

- - - - -

  • Please log in to reply
6 replies to this topic

#1
LukeEdAllen

LukeEdAllen

    Contributor

  • New Member
  • PipPip
  • 10 posts
  • United Kingdom

Hi everyone,

I have recently got my first job in GIS after finnishing university. I am working for one of my local councils digitizing planning applications and enforcements from old hardcopy (map documents & microfiche) onto Uniformlive (which I think using a stripped down version of ArcGIS).

What I wanted to ask, and what wasnt practically taught in my digitising modules at university ;) was digitising very large features on a map - for example I have been digitizing quarry boundanries that fill a 1:5000 scale map.

From my own experience doing this, the best way I have found to do it is to first zoom out to a scale where you can see the entire area or the bulk of the area that the feature occupies, and then to digitize the general shape of the feature. Once this is done I will zoom in to a large scale and clean up the overshoots and undershoots and snape them to boundary lines.

This is the only way that I feel comfortable with at the moment doing such large features - because if I try to do the digitizing straight away zoomed in at a large scale I find I lose track of the particular area of a feature I am looking at after awhile.

I just wanted to put this out there and ask if this is generally how other people digitise large features - if not please share you're experiences and tips - it would be extremely vaulable - not just for me I'm sure! :)

Thanks

Luke

Edited by LukeEdAllen, 05 December 2010 - 02:58 AM.


#2
David Medeiros

David Medeiros

    Hall of Fame

  • Validated Member
  • PipPipPipPipPipPipPip
  • 1,088 posts
  • Gender:Male
  • Location:Redwood City CA
  • Interests:Cartography, wood working, wooden boats, fishing, camping, overland travel, exploring.
  • United States

I assume your digitizing in ArcGIS or similar? I've not done much digitizing straight into a GIS program but I know it can be harder to work in and so I can see where going for a fast initial approach scaled out could help.

For my own work where I'm digitizing in Adobe Illustrator (via MAPublisher) I usually scale in pretty close to get the details done right away. I often have to zoom out to check my progress but otherwise this seems to work well for me.

I think the simple answer here is, whatever works for you is right. If your approach feels right and produces good results than you're ok, you'll figure out how to adapt and improve your workflow as you go.

GIS Reference and Instruction Specialist, Stanford Geospatial Center.

 

www.mapbliss.com

 


#3
jamesf

jamesf

    Newbie

  • Validated Member
  • Pip
  • 6 posts
  • United States

I personally like to identify where I'll use the data in the future. For example, if I'm digitizing rivers from LANDSAT for a global-scale map, I know I don't need a lot of precision at the lower zoom levels.

Now, if I'm digitizing buildings from Aerial Imagery for a city graphic...then we need more precision.

So what I do is establish roughly the scale at which my map will be presented - let's say, 1:25,000, and then after that, I'll set my digitizing scale in the dataframe properties to something like 1:15,000, so it's a bit more precise than how it'll be presented (providing your imagery/map has that resolution). This ensures that I don't digitize big polygons at a poorer resolution than the smaller ones and it also allows me to cover myself - I tag it in the metadata somewhere or a readme.txt file with my data stating that this data was digitized at XYZ scale for a graphic at ZYX scale.

Just my two cents...and I always snap polygons and lines whenever possible. I also run topologies on all applicable data to ensure I haven't overlapped or made a mistake somewhere.

#4
Kalai Selvan

Kalai Selvan

    Master Contributor

  • Validated Member
  • PipPipPipPip
  • 159 posts
  • Gender:Male
  • Location:India
  • Interests:Map Making & Map making
  • India

LukeEdAllen,

It all depends on the level of accuracy you wanted, i received a scale of 1:200000, my clients wants to get that digitized and attributed at a considerable scale, which will have a lot of bumpy lines and sharp edges, when the client wants it that way we can't help it...the same client comes out with 1:200000 scale an other map and ask us to digitize to the max detail, that means he wants each and every curve bend of the boundary to be as smooth as possible...its all based on the requirement...requirement again is based on project funding...that's how i get paid though... more the accuracy more the money and more the time....less the accuracy, less the money and less the time..

Hope thats pretty clear for you..

Thanks
GISGURU

Thanks and Regards
Kalai Selvan


#5
Nicholas_C

Nicholas_C

    Contributor

  • Validated Member
  • PipPip
  • 43 posts
  • Location:Seattle
  • United States

Here's my tips - for better or worse - assuming ArcGIS.

-zoom out the the smallest possible scale at which you can achieve the accuracy you need

-use the arrow keys to follow the feature you're tracing/editing/digitizing

-when you need to check progress, right-click on the layer you're digitizing/tracing from, and zoom to that layer

-then, use the "Go back to previous extent" button to return

-snapping, the tracing, zoom to selected features, go to previous extent, and go to next extent, are your friends

#6
frax

frax

    Hall of Fame

  • Associate Admin
  • PipPipPipPipPipPipPip
  • 2,310 posts
  • Gender:Male
  • Location:Stockholm, Sweden
  • Interests:music, hiking, friends, nature, photography, traveling. and maps!
  • Sweden

You can also have multiple views open, and/or the magnifier.
Hugo Ahlenius
Nordpil - custom maps and GIS
http://nordpil.com/
Twitter

#7
LukeEdAllen

LukeEdAllen

    Contributor

  • New Member
  • PipPip
  • 10 posts
  • United Kingdom

Thanks to everyone for contributing - I have picked up some handy tips - hopefully this post can be of some aid to others in the future too!

Thanks again!

;)




0 user(s) are reading this topic

0 members, 0 guests, 0 anonymous users

-->