Cached Map Service & the Base Map Design
The website makes use of a ‘cached’ map service. That’s how it is able to render the map so quickly.
First, what is cached? Here is a thorough description from the ESRI ArcGIS Server WebHelp. A cached map service is one that draws on your screen more immediately because it was rendered earlier instead of on-demand. Instead of waiting on our server to draw the map, your browser simply fetches the map ’tiles’ as needed instead of creating a new map for each request.
What you get is a map that displays more immediately. The trade off is less control over the scale at which data draws (they are fixed and hard coded as part of the map cache) as well as the inability to alter the visibility for layers participating in the map cache. The grayed out layers are those participating in the cached map service.
We will need to determine what map layers (ie parcels, roads, addresses, etc) can participate within a cached map service that gets updated every couple days. These cached layers will be used most often by the majority of users and always visible.
We also need to determine what the ‘dynamic’ map layers will be. These are map layers that are not used as frequently, but occasionally referenced. Once a user makes dynamic map layers visible, the website render the map a little slower. So there will be a performance hit, but will give folks the flexibility to alter or toggle visibility.
So with that said, we need some help from folks on what layers comprise the perfect ‘base’ map that balances what everyone needs at a minimum before turning other layers on dynamically.
Cartography Decisions such as:
- do addresses become visible at 2000 instead of 1000?
- when addresses are visible at 2000 are labels also visible (if they fit) within the boundary of the parcel.
- what should city limits be rendered as? does a solid grey fill work at scales at and above 8000? does the grey hatch work at 4000 and scales below?
Also, the cached basemap is ‘fused’ so that individual layers within the map are unavailable to toggle their visibility. A cached map service is designed to improve the speed the website renders the map. Any ‘dynamic’ layer causes the website to take a performance hit and renders the map slightly slower. A balance must be struck between the perfect base map and what layer visibility options exist.