Map caching concepts and terms

This is a reference topic that briefly defines some of the terms you'll encounter when reading about and working with map caches. Many of these terms are described in more detail in other help topics.

antialiasing

A graphics technique used to trick the eye into seeing smoother lines and text. You can apply antialiasing to your map caches, although there is a performance penalty for doing so. To see if antialiasing was used in an existing cache, open the tiling scheme file conf.xml and check to see if the <Antialiasing> tag is set to true.

background color

The background color of the data frame in your map document, which will be made transparent in the map cache tiles if you are using an image format that supports transparency. You should set a background color that is not used anywhere else in your map.

cache

See map cache.

cache directory

See server cache directory.

compact cache

A cache in which the tiles are grouped as a continuous binary stream of data in large files called "bundles." This reduces required storage space and cache copy time.

Convert Map Server Cache Storage Format

A geoprocessing tool that can convert compact caches to exploded storage format and vice versa.

Create Map Server Cache

A geoprocessing tool that initializes the cache and sets the tiling scheme. This tool does not create any tiles.

Delete Map Server Cache

A geoprocessing tool used for deleting a cache, its folder structure, and its associated tiling scheme file.

disconnected cache

A cache whose source data has been purposefully removed from the server. All tiles for the cache should be built before the cache is disconnected. At least one layer should remain in the source map document defining the full extent of the map.

DPI

Dots per inch. This determines the resolution of your cache tiles.

dynamic map service

A service that does not use tiles from a cache to display the map. Instead, the map is drawn by the server each time it is requested. All map services are dynamic when first created.

exploded cache

A cache in which each tile is represented by an individual image file. This was the only way to store a cache before the compact cache option was introduced at ArcGIS Server 10.

Export Map Server Cache

A geoprocessing tool used to set aside subsets of tiles that can then be imported into other caches for collaborative cache building.

fused cache

A cache in which all the layers in the map are drawn together onto the set of tiles. Consequently, layers cannot be turned on and off in a fused cache.

Import Map Server Cache

A geoprocessing tool used to bring tiles into a cache that have been exported from another cache. This is useful in collaborative caching scenarios where many organizations contribute tiles to one cache.

local cache

Cache tiles stored on a client after navigating the map. This eliminates the need to return to the server to get the tiles in the future. However, locally stored tiles can become out of sync with the tiles on the server.

Manage Map Server Cache Scales

A geoprocessing tool that adds or removes scales from an existing cache.

Manage Map Server Cache Tiles

A geoprocessing tool that creates new tiles, replaces old tiles, or deletes tiles from the cache. This tool is used for both cache creation and updates.

map cache

A set of prerendered map images stored on the server for rapid retrieval by those who view a map service. A map service can be cached or noncached. When you first create a map service, it is noncached, and you must explicitly set the cache properties and create the tiles if you want the service to be cached.

mixed mode cache

A cache in which tiles with background transparency are stored as PNG and tiles without transparency are stored as JPEG. Choose MIXED as the image format to accomplish this. Mixed mode caches are useful in some raster image overlay scenarios.

multilayer cache

A cache in which individual layers, or groups of layers, have each been drawn on a separate set of tiles. Consequently, layers can be turned on and off in a multilayer cache. Multilayer caches are not recommended for Web clients.

on-demand caching

The act of creating tiles the first time they are requested by a client, instead of precreating the tiles. On-demand caching is a good way to save space and cache creation time, but the first person who navigates to the map area will have to wait for the tiles to be drawn.

server cache directory

The location on disk where your caches are stored. You can configure cache directories on the Server Properties dialog box. When you install all the components of ArcGIS Server on a single machine, a server cache directory is configured for you.

tile

One image in a map cache.

tile height

The height of a tile in pixels. The default is 256.

tile width

The width of a tile in pixels. The default is 256.

tiling origin

The upper left point on the tiling grid. The tiling origin is usually not the point where tiles begin to be created; that only happens in the full extent of the map. Usually the tiling origin is far outside the map to ensure that the map area will be covered and that other caches with the same tiling origin can overlay your cache.

tiling scheme

The settings used to build a map cache, including scales, tiling origin, tile image format, tile size, and antialiasing. These are stored in a tiling scheme file, conf.xml, near the top folder of the cache (in the folder representing the data frame name). You can import an existing tiling scheme file when creating a new cache.

Update Mode

An important parameter in the caching tools that determines whether the tool will re-create all the tiles in the cache, create only empty tiles, or delete tiles.

virtual cache directory

A virtual directory on the Web server that references the server cache directory on disk. Associating a virtual directory with your server cache directory allows clients to request cache tiles quickly through a URL.