6 replies to this topic

[joran]

how many unique data elements would be in a medium-large size data layer? not the whole project, just one overlay layer.

Im asking because the company im working for www.cartograph.com
has an online cartographic/GIS however the system can only realistically handle datasets of 20,000-30,000 data elements per layer, and im wondering if this would be sufficient for most GIS/Cartographic purposes?

the projects themselves can have unlimited numbers of layers(well prolly about hte same 20k-30k limit), but each overlay data layer can only render 20k-30k data elements without crashing currently.

Im not sure how coherent this is, but hopefully you guys understand the essence of my question.

[benbakelaar]

do a point, line, and polygon all count as one data element, or do lines and polygons count as multiple points? for example, the borough boundaries for nyc are quite complex in areas. but they only consist of 5 polygons.

[Rob]

cartographically, 20-30K is plenty/overkill because of any data generalization the carto would assume. In the GIS realm I use data sets everyday that have more objects than your stated limits.

[joran]

do a point, line, and polygon all count as one data element, or do lines and polygons count as multiple points? for example, the borough boundaries for nyc are quite complex in areas. but they only consist of 5 polygons.

<{POST_SNAPBACK}>

A point and a ( polygon/line) cannot be on the same layer

a polygon only counts as one data element
a line is one data element
a point is one data element
but they are mutually exclusive in our system a layer with points cannot also have poly's and/or lines

you would have 3 layers one for points one for lines and one for polygons

cartographically, 20-30K is plenty/overkill because of any data generalization the carto would assume. In the GIS realm I use data sets everyday that have more objects than your stated limits.

ok cool thanks for the info. I dont really see a way around this
If i put in a function to break up a layer into several smaller layers do ou think this would be a major inconvienence to the GIS User?(I could let the user sort through the layer and seperate them into blocks of 20k or allow the user to set rules to auto split based on user entered criteria?

like instead of Mines break it down by state "ca_mines","id_mines"."mn_mines",
or even smaller "clark_cnty_lines"
or if it wasnt something quantile it could be
layer "everything" -> "everything1","everything2"

would something like this totally destroy the functionality for someone using it for GIS purposes?

what would be the largest number of data elements in a layer for a GIS user, realistically, someone using our product on a proffessional level would need to be able to have how many data elements(IN A SINGLE LAYER, not in the whole project ?)

[frax]

joran - I think you need to be careful with the terminology - when you say "cartographic" uses, I think about the preparation of separate map views (images, pdf files). I haven't looked at your service, but I think you are thinking of interactive and exploratory/browsing map uses, which could use all kinds of scales.

What technology are you using for the service - do you have a backend such as SDE/postgresql/oracle that can handle very large datasets and/or software and levels of generalization (like spatial pyramids)

[joran]

I dont think im allowed to mention specifics on the backend, but suffice it to say our backend is sound

but that feedback is exactly the kind of feedback we need. currently there is no way to output a pdf or rasterized image if you guys think thats a must(it sounds like a good idea to me) I'll run it by the backend people and see if they can whip it up.

[frax]

I still haven't check out your service - but all things that you see on the screen in the browser are rasterized images, aren't they? For faster display, the data that is presented in the display should be automatically generalized (using pyramids, prerendered images and/or layers of generalization etc)