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2013
With the growing need for organizations to distribute their data in remote locations, geodatabase replication can help to manage the changes made between geodatabases in different locations. When working with distributed and remote geodatabases it is often asked, “What is the best method to create and setup replicas?”



Working over a WAN (wide area network) or the Internet in disconnected environments is often simplified by using a geodata service to create replicas and synchronize edits for replicas. Using the Create Replica from Server tool can be useful when needing to create replicas on smaller datasets, but because this tool processes the data and replica registration in one step, it may not be a good fit for larger datasets. What is a suitable workflow to follow when the datasets to be replicated are very large?

Due to the size of data it is often not possible to create the replica using a geodata service where the data is being created and transported to the relative replica geodatabase during this replica creation process. In these cases it is better to manually transport the data from the parent geodatabase to the child location and then register the replica with the register with existing data option. The option of replicating with a disconnected workflow by creating the replica and transporting using a geodatabase or an XML workspace document is another option. Keep in mind this XML file has the potential of being very large as it will contain the data and the replica registration.

It may be better just to copy the data to the remote location first, and then create the replica registration by using the Create Replica wizard saved to an XML document that uses the 'Register with existing data' option. Then, this XML document can be imported to the child geodatabase to finalize the replica registration (use the data option on the Import XML workspace document when importing to the child geodatabase.)

In this workflow there will be an example of first transporting the data to be replicated to the destination geodatabase and then creating the replica registration via a geodata and map service with the register with existing data option.

Prerequisites


When using the register with existing data option during the replica creation, there are several things to keep in mind.
  • Geoprocessing tools like Create Replica from Server and Create Replica cannot be used with this option as it is only available in ArcMap via the Distributed Geodatabase toolbar.
  • There are several requirements or prerequisites for the data when using the 'Register with existing data option' during the replica creation / registration:
        • GlobalIDS must exist on the data that will be included in the replica prior to copying to the destination geodatabase.
        • The data must match exactly on parent and child geodatabase.
  • Please reference the Preparing data for replication and Replicas created with the option to register with existing data help topics for the tips section, which discusses important considerations.
  • Map services and geodata services must have their data sources registered as data stores prior to publishing. Please see the About registering your data with server help reference for more information about registering data stores.

Create/Register the Replica via a Geodata/Map Service


This workflow assumes that the data has previously been copied to the destination geodatabase and uses tools to register the data that are included in the replica to start tracking the changes between parent and child replica geodatabases. This data may already exist in both locations or can be easily transferred via database restore, etc. The steps use a map service to specify the exact datasets that will be registered within the replica and a geodata service component to communicate with the remote geodatabase to create/register the replica. Using the geodata enabled map service allows for the Distributed Geodatabase toolbar to become enabled to use the Create Replica tool with the register with existing data option.

Steps:

  1. Copy data to the destination geodatabase and follow all the prerequisites for distributed data/replication.
  2. Register data stores for the geodatabase that the geodata and map services will be published from.
  3. On the parent geodatabase server, publish a geodata service. (Publishing a geodata service)
  4. On the parent geodatabase server, create a map document with the data that will be included in the replica and publish this as a map service. Note: Make sure to use the same name as the geodata service and place the map service in the same location as the geodata service.
    (Publishing a map service)
  5. On the child geodatabase server, browse to the GIS Servers and add the previously created map service to a new ArcMap document. On the Distributed Geodatabase toolbar, launch the Create Replica tool and create a replica using the specific replica type needed (for example, two-way).
  6. Within the ‘What do you want to replicate?’ section, select ‘Register with existing data only’.
  7. Select the local child geodatabase within the ‘Which geodatabase do you want to replicate data to?’ section.
  8. Provide the replica with a name.
  9. Optionally, select ‘Show advanced options for overriding replica defaults when I click next’ to change the geodatabase model to full or simple and to select the Spatial extent for the replica.

After this process completes, the Replica Manager can be accessed from parent and child replica geodatabases to ensure that the replica has registered properly. The geodata service can then be used to synchronize changes when needed.

Additional Resources


Check out the ArcGIS Resource center for help topics working with Geodatabase Replication and Distributed data to learn more about different scenarios of using replication based on your organization’s needs.Melissa J – Geodata Support Analyst

"When do I use the Define Projection tool and the Project tool?," we hear you ask. Well, this blog post should be able to answer your question!

 

The Define Projection tool

Spatial data implicitly has coordinate values in either geographic or projected coordinates. A geographic coordinate system (GCS) uses a three-dimensional spherical surface to define locations on the earth; whereas, a projected coordinate system is defined on a flat, two-dimensional surface. Unlike a geographic coordinate system, a projected coordinate system has constant lengths, angles, and areas across the two dimensions. However, we need to explicitly define the coordinate system of our data. If  we have undefined data, then we can use the Define Projection tool to define it. Otherwise, when data without a defined spatial reference is added to ArcMap, a dialog box will display that lists the data sources that are missing spatial reference information.

figure_one_new1.png

Figure 1: Dataset missing Spatial Reference

If the data that you added to ArcMap has coordinate values that are projected, 'Unknown Units' will be displayed next to your coordinates in the data view until the projected coordinate system is defined.

NEW_FIGURE_21.png

Figure 2: The units are listed as Unknown



If the dataset that you added to ArcMap has geographic coordinates, the units will still display as ‘Decimal Degrees’ or in Degrees, Minutes and Seconds (DMS) (e.g. 82°45'46.8"E 41°44'56.4"N) even though the datum has yet to be defined. This is because latitude and longitude values always have angular units.
NEW_FIGURE_31.png

Figure 3: The Decimal Degrees units are displayed even though it's undefined



Defining a geographic or projected coordinate system for a shapefile, Esri Grid format, raster dataset (TIFF, JPG) or a file geodatabase does not require you to output to a new dataset. The Define Projection tool updates your existing dataset by creating an associated file (e.g. .prj, prj.adf,.aux). For personal geodatabases, the spatial reference table is updated.

For shapefiles, Esri Grids, raster datasets, and file/personal geodatabase feature classes you will need to go to ArcToolbox > Data Management Tools > Projections and Transformations > Define Projection to assign a geographic or projected coordinate system to your dataset.

A principle of good data management is to obtain the projected or geographic coordinate system parameters from your data source provider or associated metadata. It is strongly advised that you do not make an educated guess about the coordinate system of your data, as an inaccurate GIS database usually results. However, if you do not have access to the data source provider you can try using the steps in Esri Knowledge Base Article 24893 to identify an unknown projected coordinate system using ArcMap.

 The Project tool

To change from one coordinate system to another, use the Project tool from ArcToolbox. When using the Project tool a new output dataset is created.

For shapefiles and feature classes, you will need to go to ArcToolbox > Data Management Tools > Projections and Transformations > Feature > Project to transform your dataset to another coordinate system.

Project_the_Feature.png

Figure 4: The Project tool

 To project multiple shapefiles or feature classes:

  1. Right-click the Project tool and select the Batch mode.
  2. Select the shapefile or feature class to be projected.
  3. Specify a location and name for the new projected data.
  4. If you're using the Batch mode of the Project tool, double-click the output dataset cell to browse to a location and save.

After specifying the location and name for the new projected data, specify the output coordinate system to project the data. If it is required, select an optional geographic transformation and complete the projection!

Additional Resources

For more information, refer to these articles:

HowTo: Project shapefiles or geodatabase feature classes with the ArcToolbox Project wizard or Tool

FAQ: Projection Basics: What the GIS professional needs to know

How To: Select the correct geographic (datum) transformation when projecting between datums

Rajeshwary K. - Online Support Resources


Tuning your RDBMS is an important aspect of maintaining your enterprise geodatabase. Two tasks found in all Esri-supported RDBMS are updating DBMS statistics and rebuilding indexes. If you are loading data in bulk or running query-intensive DML operations with SQL, these tasks need to be done more often. Fortunately for us, these tasks are relatively straightforward to accomplish.



The scripts found in Esri Knowledge Base Article 24518 provide the SQL to both update statistics and rebuild indexes.

NOTE:
  • Oracle databases can be set to automatically update statistics.
  • The SQL Server script in KB24518 is still applicable for geodatabases in SQL Server 2008, 2008R2 and 2012.

Also, if you are using ArcGIS 10.2 or 10.1, there are some new geoprocessing tools in the ArcToolbox that can accomplish this:Data Management Tools > Geodatabase Administration > Analyze Datasets:
Updates the database statistics of base tables, delta tables, and archive tables, along with the statistics on those tables’ indexes. This tool is used in enterprise geodatabases to help get optimal performance from the RDBMS query optimizer. Stale statistics can lead to poor geodatabase performance.Data Management Tools > Geodatabase Administration > Rebuild Indexes:
Updates indexes of datasets and system tables stored in an enterprise geodatabase. This tool is used in enterprise geodatabases to rebuild existing attribute or spatial indexes. Out-of-date indexes can lead to poor geodatabase performance.

No matter which one you choose, these resources can be run as automated tasks using SQL, or the ArcToolBox tools can be exported to Python and automated as well.Ken G. - Geodata Support Analyst

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