ArcGIS.com Help - Performing analysis

Imagine you've been tasked to evaluate potential sites for a new warehouse. This evaluation is to be based on access to transportation, the presence of special restrictions such as nearby historical neighborhoods, access to restaurants and other facilities that employees may need, access to public transportation for employees, and nearby land use that may restrict or enhance development. How do you evaluate these sites in a quantifiable and defensible way? Of course you need data, but you also need tools that can analyze and measure geographic relationships.

Whenever you look at a map, you inherently start turning that map into information by finding patterns, assessing trends, or making decisions. This process is called spatial analysis, and it's what our eyes and minds do naturally whenever we look at a map.

But many patterns and relationships aren't always obvious by looking at a map. Often, there's too much data to sift through and present coherently on a map. The way you display the data on the map can change the patterns you see. Spatial analysis tools allow you to quantify patterns and relationships in the data and display the results as maps, tables, and charts. The spatial analysis tools that are now part of ArcGIS Online empower you to answer questions and make important decisions using more than a visual analysis.

To learn more about accessing and running the tools, see Using the analysis tools. An overview of each of the tools is available in the section below.

If you're a developer, you can access these tools via web APIs. For more information, see the Spatial Analysis Service REST API.

Available analysis tools

The analysis tools are arranged in categories. These categories are logical groupings and do not affect how you access or use the tasks in any way.

Summarize data

These tools calculate total counts, lengths, areas, and basic descriptive statistics of features and their attributes within areas or near other features.

Tool	Description
Aggregate Points	This tool works with a layer of point features and a layer of area features. It first figures out which points fall within each area. After determining this point-in-area spatial relationship, statistics about all points in the area are calculated and assigned to the area. The most basic statistic is the count of the number of points within the area, but you can get other statistics as well. For example, suppose you have point features of coffee shop locations and area features of counties, and you want to summarize coffee sales by county. Assuming the coffee shops have a TOTAL_SALES attribute, you can get the sum of all TOTAL_SALES within each county, or the minimum or maximum TOTAL_SALES within each county, or the standard deviation of all sales within each county.
Summarize Nearby	This tool finds features within a specified distance of features in the analysis layer. Distance can be measured as a straight-line distance, a drive-time distance (for example, within 10 minutes), or a drive distance (within 5 kilometers). Statistics are then calculated for the nearby features. For example: Calculate the total population within five minutes of driving time of a proposed new store location. Calculate the number of freeway access ramps within a one-mile driving distance of a proposed new store location to use as a measure of store accessibility.
Summarize Within	This tool finds features (and portions of features) within the boundaries of areas in the analysis layer. For example: Given a layer of watershed boundaries and a layer of land-use boundaries by land-use type, calculate total acreage of land-use type for each watershed. Given a layer of parcels in a county and a layer of city boundaries, summarize the average value of vacant parcels within each city boundary.

Tool

Description

Aggregate Points

Aggregate Points

This tool works with a layer of point features and a layer of area features. It first figures out which points fall within each area. After determining this point-in-area spatial relationship, statistics about all points in the area are calculated and assigned to the area. The most basic statistic is the count of the number of points within the area, but you can get other statistics as well.

For example, suppose you have point features of coffee shop locations and area features of counties, and you want to summarize coffee sales by county. Assuming the coffee shops have a TOTAL_SALES attribute, you can get the sum of all TOTAL_SALES within each county, or the minimum or maximum TOTAL_SALES within each county, or the standard deviation of all sales within each county.

Summarize Nearby

Summarize Nearby

This tool finds features within a specified distance of features in the analysis layer. Distance can be measured as a straight-line distance, a drive-time distance (for example, within 10 minutes), or a drive distance (within 5 kilometers). Statistics are then calculated for the nearby features. For example:

Calculate the total population within five minutes of driving time of a proposed new store location.
Calculate the number of freeway access ramps within a one-mile driving distance of a proposed new store location to use as a measure of store accessibility.

Summarize Within

This tool finds features (and portions of features) within the boundaries of areas in the analysis layer. For example:

Given a layer of watershed boundaries and a layer of land-use boundaries by land-use type, calculate total acreage of land-use type for each watershed.
Given a layer of parcels in a county and a layer of city boundaries, summarize the average value of vacant parcels within each city boundary.

Data enrichment

These tools help you explore the character of areas. Detailed demographic data and statistics are returned for your chosen areas. Comparative information can also be reported for expanded areas such as counties and states.

Tool	Description
Enrich Layer	This tool enriches your point or area data by getting facts about the people, places, and businesses that surround your data locations. Enrich Layer enables you to answer new questions about locations that you cannot answer with maps alone; for example, What kind of people live here? What do people like to do in this area? What are their habits and lifestyles? What kind of businesses are there in this area? The result will be a new layer containing all demographic and geographic information from given data collections. This new information is added as fields in the table.

Tool

Description

Enrich Layer

Enrich Layer

This tool enriches your point or area data by getting facts about the people, places, and businesses that surround your data locations. Enrich Layer enables you to answer new questions about locations that you cannot answer with maps alone; for example, What kind of people live here? What do people like to do in this area? What are their habits and lifestyles? What kind of businesses are there in this area?

The result will be a new layer containing all demographic and geographic information from given data collections. This new information is added as fields in the table.

Analyze patterns

These tools help you identify, quantify, and visualize spatial patterns in your data by identifying areas of statistically significant clusters.

Tool	Description
Find Hot Spots	The Find Hot Spots tool will determine if there is any statistically significant clustering in the spatial pattern of your data. Are your points (crime incidents, trees, traffic accidents) really clustered? How can you be sure? Have you truly discovered a statistically significant hot spot (for spending, infant mortality, consistently high test scores) or would your map tell a different story if you changed the way it was symbolized? The Find Hot Spots tool will help you answer these questions with confidence.

Tool

Description

Find Hot Spots

The Find Hot Spots tool will determine if there is any statistically significant clustering in the spatial pattern of your data.

Are your points (crime incidents, trees, traffic accidents) really clustered? How can you be sure?
Have you truly discovered a statistically significant hot spot (for spending, infant mortality, consistently high test scores) or would your map tell a different story if you changed the way it was symbolized?

The Find Hot Spots tool will help you answer these questions with confidence.

Use proximity

These tools help you answer one of the most common questions posed in spatial analysis: "What is near what?"

Tool	Description
Create Buffers	A buffer is an area that covers a given distance from a point, line, or area feature. Buffers are typically used to create areas that can be further analyzed using a tool such as Overlay Layers. For example, if the question is "What buildings are within one mile of the school?", the answer can be found by creating a one-mile buffer around the school and overlaying the buffer with the layer containing building footprints. The end result is a layer of those buildings within one mile of the school.
Create Drive-Time Areas	Create Drive-Time Areas creates areas that can be reached within a specified drive time or drive distance. It measures out from one or many points (up to 1,000), along roads, to create a layer that can help you answer questions such as: Where can I go from here within a 30-minute drive? Where can I go from here within a 30-minute drive at 5:30 p.m. during rush hour? What areas of town can the fire department reach within five minutes? How would fire-response coverage improve by building a new fire station here? What market areas does my business cover? You may be able to answer your questions solely through visualizing the output areas. Alternatively, you can perform further spatial analysis using the output areas. For instance, running Aggregate Points using drive-time areas with demographic data can help determine which potential store location would likely provide the best customer base for your type of business.
Find Nearest	This tool finds the nearest features and, optionally, reports and ranks the distance to the nearby features. To find what's nearby, the tool can either measure straight-line distance, road distance, or driving time. There are options to limit the number of nearest features to find or the search range in which to find them. The results from this tool can help you answer the following kinds of questions: What is the nearest park from here? Which hospital can I reach in the shortest drive time? How long would the trip take on a Tuesday at 5:30 p.m. during rush hour? What are the road distances between these major cities? Which of these patients reside within two miles of these chemical plants? Find Nearest returns a layer containing the nearest features and, optionally, a line layer that links the start locations to their nearest locations. The optional line layer contains information about the start and nearest locations and the distances between.

Tool

Description

Create Buffers

A buffer is an area that covers a given distance from a point, line, or area feature.

Buffers are typically used to create areas that can be further analyzed using a tool such as Overlay Layers. For example, if the question is "What buildings are within one mile of the school?", the answer can be found by creating a one-mile buffer around the school and overlaying the buffer with the layer containing building footprints. The end result is a layer of those buildings within one mile of the school.

Create Drive-Time Areas

Create Drive-Time Areas creates areas that can be reached within a specified drive time or drive distance. It measures out from one or many points (up to 1,000), along roads, to create a layer that can help you answer questions such as:

Where can I go from here within a 30-minute drive?
Where can I go from here within a 30-minute drive at 5:30 p.m. during rush hour?
What areas of town can the fire department reach within five minutes?
How would fire-response coverage improve by building a new fire station here?
What market areas does my business cover?

You may be able to answer your questions solely through visualizing the output areas. Alternatively, you can perform further spatial analysis using the output areas. For instance, running Aggregate Points using drive-time areas with demographic data can help determine which potential store location would likely provide the best customer base for your type of business.

Find Nearest

This tool finds the nearest features and, optionally, reports and ranks the distance to the nearby features. To find what's nearby, the tool can either measure straight-line distance, road distance, or driving time. There are options to limit the number of nearest features to find or the search range in which to find them. The results from this tool can help you answer the following kinds of questions:

What is the nearest park from here?
Which hospital can I reach in the shortest drive time? How long would the trip take on a Tuesday at 5:30 p.m. during rush hour?
What are the road distances between these major cities?
Which of these patients reside within two miles of these chemical plants?

Find Nearest returns a layer containing the nearest features and, optionally, a line layer that links the start locations to their nearest locations. The optional line layer contains information about the start and nearest locations and the distances between.

Manage data

These tools are used for both the day-to-day management of geographic data and for combining data prior to analysis.

Tool	Description
Extract Data	With this tool, you can select and download data for a specified area of interest. Layers that you select will be added to a zip file or layer package.
Dissolve Boundaries	Areas that overlap or share a common boundary are merged together to form a single area. You can control which boundaries are merged by specifying a field. For example, if you have a layer of counties, and each county has a State_Name attribute, you can dissolve boundaries using the State_Name attribute. Adjacent counties will be merged together if they have the same value for State_Name. The end result is a layer of state boundaries.
Merge Layers	This tool copies features from two layers into a new layer. The layers to be merged must all contain the same feature types (points, lines, or areas). You can control how the fields from the input layers are joined and copied. For example: I have three layers for England, Wales, and Scotland, and I want a single layer of Great Britain. I have 12 layers and each contains parcel information for contiguous townships. I want to join them together into a single layer, keeping only the fields that have the same name and type on the 12 input layers.
Overlay Layers	Overlay Layers combines two or more layers into one single layer. You can think of overlay as peering through a stack of maps and creating a single map containing all the information found in the stack. In fact, before the advent of GIS, cartographers would literally copy maps onto clear acetate sheets, overlay these sheets on a light table, and hand draw a new map from the overlaid data. Overlay is much more than a merging of line work; all the attributes of the features taking part in the overlay are carried through to the final product. Overlay is used to answer one of the most basic questions of geography, "What is on top of what?" For example: What parcels are within the 100-year floodplain? (Within is just another way of saying on top of.) What roads are within what counties? What land use is on top of what soil type? What wells are within abandoned military bases?

9/23/2013