[mapguide-users] RE: Guidelines for using Base Layers

[Jackie Ng]

Hi Kori,

Thanks for this useful information. Cheers.

- Jackie


Kori Maleski-2 wrote:
> 
> Hi Jackie,
> 
> In general, what I would recommend:
> 
> Tile what you would consider non-interactive layers.
> i.e.  
> For a municipal application 
> Tiled - Hydrology, Parks, Street network, Boundaries
> Un-tiled - Storm, Sanitary and Water networks
> Parcel fabric will perform better tiled, but you may wish the user to have
> the ability to turn off or on.
> 
> Raster Aerial/Satellite imagery layers will perform better when tiled as
> well, but will not necessarily be visible under a Tiled base layer (which
> itself a raster).
> To alleviate this, what you can do is prepare 2 tiled base layers. One
> with
> the raster aerial and the other recommended vector layers; and then one
> without the raster - vector only.  In this way you have control over where
> in the layer ordering the raster aerial displays.  In the legend you would
> make the Base layer group with the raster visible, but off by default,
> labeled "Aerial imagery" etc. and then leave the vector only Base layer
> group on by default and not visible in the legend.  These preferences are
> up
> to you and/or your client.  
> 
> You can just use the raster layers without tiling, as the FDO provider
> will
> perform adequately, but you may have layer ordering issues with Base Tiled
> layers.  You should be aware that the speed/display performance will be
> better tiled.
> 
> To summarize, you layer ordering should/could be something like this:
> 
> Interactive Layers:
> 	Hydrants
> 	Valves
> 	Manholes
> 	Water Main
> 	Storm Main
> 	Sanitary Main
> 	Parcels
> Base Tiled Layer Group - With Raster (equivalent to Google's Hybrid view):
> 	Street Centre line
> 	Lakes (optional as you may not wish to obscure imagery)
> 	Rivers (optional as you may not wish to obscure imagery)
> 	Parks (Boundary with no fill)
> 	Neighborhood Boundaries
> 	City Boundaries
> 	Aerial Imagery
> Base Tiled Layer Group - Vector only (equivalent to Google's Map view):
> 	Street Centre line
> 	Lakes
> 	Rivers
> 	Parks
> 	Neighborhood Boundaries
> 	City Boundaries
> 
> You could also have a Base Tiled layer with the Raster Aerial Only, or
> just
> an interactive raster layer and the is would be equivalent to Google's
> Satellite view.  Thus giving the same options as Google, but with the
> ability to overlay (as in my example above) client data.
> 
> Thematics such as zoning or statistical census layers can complicate the
> process - you may wish to leave them in the interactive group under/over
> the
> parcels.
> 
> 
> How many zoom thresholds is dependant on the aerial extent of your map.
> Google uses 20 for a continental/world view.
> 
> You could use 10 for New South Wales and then 15-20 for Western Australia,
> because the extent differences.
> 
> For a municipal sized application, you could use 10 for a Sydney sized map
> or 5 for an area like Parramatta.  
> 
> It all depends on how far you want to zoom in as well.  Google does not
> zoom
> in close enough for good parcel detail - such as the labeling of frontage
> or
> parcel perimeter.  That may require a few more thresholds.
> 
> Best thing to do, is to test with the ajax viewer - zoom in to an existing
> map to what you perceive as the minimum zoom, and just click/zoom out till
> you reach you maximum zoom ideal.  Count how many times you zoomed.  Start
> with that.  If you perceived too many zooms then reduce the number you
> would
> use.  In the base layer tiling dialog - enter your desired minimum and
> max,
> set the number of zoom thresholds, save the map and test.
> 
> Pre-generation will have to be done anytime the MAP is saved, as the tile
> cache is AUTOMATICALLY erased upon a map save (at least with the last
> version of MGO). 
> 
> You can pre-generate by zooming and panning around to build your cache, or
> by using a programmed application.
> 
> We will be releasing a free tiling application to the community shortly. 
> 
> Cheers,
> 
> 
> Kori Maleski
> 
>  
> 
>  
> 
> -----Original Message-----
> From: mapguide-users-bounces at lists.osgeo.org
> [mailto:mapguide-users-bounces at lists.osgeo.org] On Behalf Of Jackie Ng
> Sent: April 16, 2007 10:30 AM
> To: mapguide-users at lists.osgeo.org
> Subject: [mapguide-users] Guidelines for using Base Layers
> 
> 
> Hi All,
> 
> I'm a noob to Base/Tiled Layers in MapGuide. 
> 
> Are there any guidelines or rules of thumb to using Base (Tiled) Layers?
> 
> - How many zoom levels to make?
> - Tile everything or only certain layers?
> - I've read about pre-generating tiles. If I pre-generate tiles, how often
> should I do this?
> - etc...
> 
> Regards,
> 
> - Jackie
> 
> 
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