ArcGIS Topology Shapefiles, Coverages, Geodatabases Friday 03/03/06 GEOG 4103

Topology in GIS generally defined as the spatial relationships between adjacent or neighboring features implemented through data structure

Components Connectivity: Arcs are connected to others (at nodes). This identifies possible routes and networks, such as rivers and roads.. Containment: An enclosed polygon has a measurable area; lists of arcs define boundaries and closed areas. Contiguity: The adjacency of polygons can be determined by shared arcs.

Polygon A has arcs a1,a2, a3 Node 1 is connected with arcs a2, a1, a6 arc a5 has polygons C (right) and B (left)

Data Structures COVERAGE Files are stored in two directories Coverage name – unique files for the coverage INFO – files for all the coverages in that workspace/directory Exchanged using ARC/INFO Exchange Files (.E00)

Coverages Coverages can be point, line or polygon A single coverage can have points and lines, or lines and polygons, but never points and polygons Polygon coverages partition the area into polygons No overlap allowed between polygons All areas in the coverage are part of some polygon

Coverages Coverages are created using the BUILD and CLEAN commands CLEAN attempts to fix problems in topology, sometimes moving points and lines BUILD assumes the topology is “clean” and fails if topological problems are encountered It creates Point, Arc and Polygon attribute tables (PAT, AAT)

Arc Attribute Table (AAT) arcs have attributes which identify the polygons on either side "left" and "right" by reference to the sequence in which the arc is coded topological relationships stored in AAT I.e. adjacent polygon IDs in the LPoly and RPoly fields.

Grids Deal with RASTER (gridded) data Each grid cell contains a single number Files are stored in several directories, so to move a grid it is safest to EXPORT it Grids have a .VAT or Value Attribute Table that relate codes in the grid to associated attributes

Shapefiles Shapefiles Comprised of 4 files – coverage.shp, .sbn, .sbx and .dbf The .dbf file contains the attribute data and can be opened with Excel, Access and other database editors that understand the .dbf format

Shapefiles Polygons in shapefiles CAN overlap, while in a COVERAGE they CANNOT so: to convert SHAPEFILES to COVERAGES Overlaps need to be eliminated

Geodatabases “Geodatabase = An object-oriented geographic database that provides services for managing geographic data. E.g relationships, and topological associations. contains feature datasets and is hosted inside of a relational database management system.”

Geodatabases Geodatabases are stored in relational databases Many large GIS users have large Oracle-based database systems that are used for GIS data using the ESRI Spatial Database Engine for conversion You can also have “Personal Geodatabases” that are maintained on the local machine

ArcGIS Components ArcCatalog ArcMap ArcToolbox ArcScene Manage data Create maps Analysis ArcToolbox Stand-alone Analysis and Conversion ArcScene 3-D display

ArcCatalog

ARCGIS Components ARC Catalog

ArcCatalog Locate Data for use with ARCGIS What data is available? Local Disks Databases Internet/Online What are the properties of that data?

ArcCatalog - Preview Preview Geodata and Tables

Metadata ArcCatalog will also display or allow editing of simplified Metadata

ArcMap

ARGIS Components ARCMAP

ArcMap advantages better map quality Projections Automatically reprojects data to match the map projection (now you can mix and match UTM and Lat-Lon coverages) But only if the source projection is defined Transparency: can see through one layer

ArcMap Toolbars Movable toolbars You select the toolbars you want from the View menu

Toolbars can be moved or put in separate windows

Tips Adding more buttons (customizing ArcMap) Continuous pan/zoom

ArcToolbox

ArcToolbox The ArcToolbox component of ArcGIS contains sets of stand-alone wizards designed to help you perform specific tasks

ArcScene

ArcScene – 3 D Data Viewer ArcScene is a 3-D data viewer that allows you to get different perspectives on three-dimensional landscapes Tilt and rotate View from a point

ArcReader Free!

ArcReader ArcReader is a FREE stand-alone tool designed for DISPLAY and printing of local and web-accessible geodata It requires that the map to be displayed be “published” to a special PMF file using an ARCGIS extension