Analyzing a Layer for Which You Have a Reference Map

Assume that you have a layer that contains the block groups for the US Census Bureau for the entire United States. This information is stored in a table called US, in a column called GEOMETRY. The extents of this layer (in the USER_SDO_GEOM_METADATA view) are -90 to 90 and -180 to 180. You also have a simple world geometry. It is stored in a table called WORLD, in a column called GEOMETRY. It too has the extents of -90 to 90 and -180 to 180. Both of these layers are indexed.

You start the Spatial Index Advisor. In the Add Layer dialog box, you select the layer WORLD(GEOMETRY). The layer alias is set to WORLD and the color is set to black After you click OK, the application does the following:

You know that this is a small geometry, so you click Draw all Geometries in Viewport toolbar button (or select Layer > Draw Geometries in Layer, then select All of the geometries). After you confirm that you want to perform the operation, the geometries are drawn in the viewport.

You then click the Zoom to Rectangle toolbar button (or select View > Zoom to > Rectangle). You draw a box around the New England states, and click the Add Layer toolbar button (or select Layer > Add Layer). You select the layer US(GEOMETRY); US is filled in as the layer alias, and the color is set to blue. After you click OK, US is the current layer.

You click the Zoom to Reasonable Size toolbar button (or select View > Zoom to > Reasonable Size). You move the pointer to a desired location, such as the center of New Hampshire, and click.

After the zoom operation is completed, you want to see how this area is indexed, so you click the Show Fixed-Sized Tiles toolbar button (or select Index > Show Fixed-size Tiles). The Tips area contains information about how to evaluate the display.

Assume that there is too little data in the tiles, and that after panning around the layer you notice that most of the tiles contain a lot of while space. You decide you should to increase the tiling level.

You now want to examine the hybrid index. You turn off the display of fixed-size tiles and click the Show Variable-Sized Tiles toolbar button (or select Index > Show Variable-size Tiles). Assume that the Tips area contains a recommendation to increase the number of tiles per geometry to 8.

You select Index > Modify Index, and based on your actions and the displayed tips, you increase the tiling level to 8 and the number of tiles to 8.

See also: Usage scenarios, Main help topics (outline)