ArcGIS Python Mapping Module

Arc Python to interact with Arc-map

What is ArcPy Mapping and Why is it actually used for :

Arcpy.mapping was built for the professional GIS analyst (as well as for developers). Traditionally, the scenarios listed above had to be done using ArcObjects and it often proved to be a very difficult programming environment to learn for the average GIS professional. Arcpy.mapping is a courser-grained object model, meaning that the functions are designed in a way that a single arcpy.mapping function can replace many lines of ArcObjects code. The following is a very simple example of how arcpy.mapping can be used to reference an existing map document and export it to a PDF document with only two lines of code.

To explore the Overall Arcpy mapping Module use the following PDF:

Arcpy Python Mapping Module

Code for Getting the reference to the MXD :

YourMXD= arcpy.mapping.MapDocument("path to the MXD")

To export the above MXD to PDF using arcpy:

arcpy.mapping.ExportToPdf(YourMXD,"your pdf file")

Pointer to a MXD present on the Disk

Layout View of the Map Document

Arcpy.mapping is not a replacement for ArcObjects but rather an alternative for the different scenarios it supports. ArcObjects is still necessary for finer-grain development and application customization, whereas arcpy.mapping is intended for automating the contents of existing map documents and layer files.

Performance issues on ArcGIS Geoprocessing Service

How to improve Geo-processing Execution Speed

Geoprocessing services hosted in the ArcGIS server needs to be pretty fast and accurate. User will always want the service to be the fastest. Since ArcGIS Server will be able to service multiple users at one instant of time, inefficient services can overload your server and increase the processing time. The more efficient and intelligent your services, the more users can be serviced with the same computing resources at a smaller amount of time.

Below are some of the tips and techniques that helps in increasing the performance of your Geo-processing Services.

Use local paths to data and resources

The more faster the data requires to be processed is accessible by the server the more faster your service will be.It is good to copy your data to the server rather than placing it on the shared location and asking the server to access it.(Copying the server will be effective only if the Geo processing input data is very small in size and also when the input data is not dynamic)

Reading data from the local area network will be slow compared to accessing the data from the local disk.. 

Reading and Writing the Intermediate data IN_Memory

The service execution speed will get increased by multiple times when the intermediate data is allowed to stored in the machine memory(RAM).Input and output operation is the slowest of all the computing operations.In Geoprocessing storing the intermediate data in a file geodatabase or personnel Geodatabase will take maximum of the execution time.

Please be sure the data which your are storing in the memory as an intermediate data need not be necessary after the execution is complete.Because once the execution is complete the data in the memory will get cleared.Don't write large amount of data to the in_memory as it may affect the performance of the processing service.

To write to your computer's memory, use the pathname in_memory, as follows:

          in_memory\your featureclassname

Use layers from a source map document

If a service uses a source map document instead of feature classes and datasets, it will tremendously increase the performance of the service.Your models and scripts can use map layers from the source map document so that it will impose less load on the processor and significantly decrease the execution time. A layer references a dataset on disk or feature class on a geodatabase, and some layers cache properties about the dataset. Therefore by using dataset layer instead of the direct dsataset or feature class,there is a performance advantage because ArcMap opens the dataset once, caches basic properties of the dataset, and keeps the dataset open. When the Service executes, the dataset need not to be  reopened because the source map document already it is opened and it will gives us a performance boost.

Write data to shapefiles

Storing the data to shapefiles is a bit faster than writing to other formats but writing data to memory, described above, is the fastest of all. Even then there is further more limitations on the shapefiles such field names should be  as 10 character , no null values, and limited support for date/time, to name a few. This become more helpful if the you are running your model locally on your Desktop

Custom Geoprocessing Tool

Arcobjects Geoprocessing Procedure:

1. Create a geoprocessor object and set its properties.
2. Set the appropriate values for the tool’s parameters.
3. Execute a tool using the geoprocessor object’s Execute() method.

In order to create a geoprocessor object, the IGeoProcessor2 interface can be used. This interface
is defined in the geoprocessing library of ArcObjects and is implemented by the GeoProcessor
CoClass.

IGeoProcessor2 gp = new GeoProcessorClass();
//add the result of geoprocessing as a new layer to Map
gp.AddOutputsToMap = true;
//if output of geoprocessing exists before the execution of tool
//it will be overwritten
gp.OverwriteOutput = true;

Assume that you want to create Thiessen polygons for the cities FeatureClass to create proximal
zones for all cities. The proximal zones represent full areas where any location inside the zone is
closer to its associated city than any other city. Based on the Create Thiessen Polygons reference
page, you have to provide at least an input point FeatureLayer and the path to the output
FeatureClass.
In order to create and set each parameter, the IVariantArray interface of the System library must
be used.

IVariantArray parameters = new VarArrayClass();

Each parameter has to be added to the IVariantArray interface in the exact order that is specified
on the tool’s reference page.

//in_features
parameters.Add(@"D:\DataFolder\fileGDB.gdb\cities");
//out_feature_class
parameters.Add(@"D:\DataFolder\fileGDB.gdb\citiesThiessen");
//fields_to_copy(Optional)
parameters.Add("ALL");

As it is illustrated on the Create Thiessen Polygons reference page, the third parameter is optional.
You can simply not add any value to IVariantArray or, as shown in the preceding code, you can
provide an appropriate value for the optional parameter. You can skip the optional parameter
using an empty string as input to IVariantArray’s Add() method. For example, look at the
reference page of the Buffer tool; you can see that three of the seven available parameters are
mandatory. The following code demonstrates how to skip the fourth parameter and specify the
fifth parameter:

//1-in_features
parameters.Add(@"D:\test.gdb\cities");
//2-out_feature_class
parameters.Add(@"D:\test.gdb\citiesBuffer");
//3-buffer_distance_or_field
parameters.Add("50 kilometers");
//4-line_side(Optional)
parameters.Add("");
//5-line_end_type(Optional)
parameters.Add("ROUND");
//6 &7 there is no need to provide empty string
//for the rest of parameters since you don't want to set them
After setting all the required parameters, all you need to run a tool is to call the Execute() method
of the geoprocessor object. The Execute() method solicits the name of the tool and its parameters.

gp.Execute("CreateThiessenPolygons_analysis", parameters, null);
The following code shows the complete code for this example. In order to run the code, you need to
add references to the Geoprocessing and System libraries of ArcObjects:
IGeoProcessor2 gp = new GeoProcessorClass();
//add the result of geoprocessing as a new layer to Map
gp.AddOutputsToMap = true;
//if output of geoprocessing exists before the execution of tool
//it will be overwritten
gp.OverwriteOutput = true;
IVariantArray parameters = new VarArrayClass();
//in_features
parameters.Add(@"D:\DataFolder\fileGDB.gdb\cities");
//out_feature_class
parameters.Add(@"D:\DataFolder\fileGDB.gdb\citiesThiessen");
//fields_to_copy(Optional)
parameters.Add("ALL");
//or parameters.Add("");
gp.Execute("CreateThiessenPolygons_analysis", parameters, null);


The Geoprocessing library of ArcObjects is accessible through the ESRI.ArcGIS.Geoprocessing
namespace. This library contains a few hundred types which can be used to run and manage tools
and GIS workfl ows. You learned earlier in this section that IGeoProcessor2 is the main interface of
this library and the easiest way to run a geoprocessing tool is to call its Execute() method.
However, using IGeoProcessor2 is not the only approach to run a geoprocessing tool or model.
There are some managed assemblies created by Esri to performing geoprocessing in a managed
way. A managed way means there is a native .NET assembly (the Geoprocessor assembly) that is
a wrapper for some types in the Geoprocessing library of ArcObjects, and there are other .NET
assemblies for each system toolbox.
These native .NET assemblies provide an even easier way to run a system tool. In general, the
procedure for running a tool using the Geoprocessor-managed assembly is the same as running a tool