[mapguide-users] Guidelines for using Base Layers

[Kori Maleski]

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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