Building Base Maps

1
Building Base Maps
2
Managing large image collections

• Large images can easily exceed the 2-GB limit on
  file size
• ESRI offers two major ways to manage spatially
  tiled images
• Image Catalogs
• ArcSDE Rasters (has 5 ways to handle, but beyond
  scope of this class)

3
Raster (a.k.a Image) Catalogs

• Group of raster files covering a similar theme
  and sharing coordinate system
• Often same format and symbology
• Examples
• Map series (DRGs)
• Orthophotos (DOQs)

4
Raster Catalogs

• Display multiple rasters without having to merge
  them into larger rasters
• Supported very well in ArcView 3
• Supported in ArcPlot, but cant do a transparent
  NODATA
• Also supported in ArcMap, but you need a script
  to do transparent NODATA

5
Raster Catalogs

• Format any table with columnsIMAGE, XMIN,
  YMIN, XMAX, YMAX
• IMAGE is a pathname to the raster
• Symbology from first raster in catalog
• ArcObjects Online sample code exists to help in
  symbolizing catalogs

6
Working with Image Catalogs

• Prerequisites
• Images in supported formats
• Georeferenced, spatial reference specified in
  ArcCatalog
• All images must use the same colormap
• If overlapping, need a special value for overlaps
  or NODATA areas

7
Image Catalog ProceduresDRG Example

• Get DRGs. Best source NRCS state offices on CD
• Decide on projection, datum
• Clip_project_DRG.aml
• Project if necessary
• Trim collars
• Assign spatial reference BatchRasterSpatialRef.ba
  s
• Use a system variable for base of paths in image
  catalog for portablility

8
Create Image Catalogs

• Arc CREATECATALOG command
• Arc ADDIMAGE command
• Drgcatalog.aml does both, adds all images in a
  folder to the catalog
• Folder2ImageCatalog.bas works in ArcCatalog, can
  do .SID files
• Other AMLs
• copyimagecat.aml (copies images)
• trimimagecat.aml (deletes images from disk)

9
Raster Catalog Pitfalls

• Make sure all files and folders are NOT read-only
• Do NOT load into ArcMap until you are sure all
  paths are correct and all images have spatial
  references
• If you load it with a bad spatial reference you
  will never be able to load it correctly

10
Changing Symbology for an Raster Catalog

• No Symbology tab
• Theres no way to store a transparent color in a
  TIFF colormap
• Must use a script to get a renderer from one
  image, apply it to all
• ChangeCatalogSymbology.bas

11
Other base maps

• NLCD
• Shaded relief at both 90- and 30-meter
  resolutions
• Precip, other layers used
• Make these TIFFs, they work better in ArcIMS