2012 Emergency Track, Emergency Preparedness: Using Local and Federal Data and ArcGIS to Analyze Potential Human and Economic Impacts of Flooding, Valerie Johnson
This presentation focuses on a case study of river flooding in Reno, Nevada. However, the "how-to" information covered is applicable to any community that experiences disasters. Floods have negative impacts on people and businesses located in flood-prone areas, as well as on the finances of local governments. It's important for emergency management staff to have knowledge of current demographics of citizens who are at risk from flooding. Residents who are elderly, lack transportation, and have fewer financial savings and resources may require special emergency response measures. Decision-makers benefit from advance knowledge about the number of and current values of commercial and residential buildings located in flood-prone areas, because their losses could impact local governments' tax revenue.
This session discusses how GIS professionals can 1) perform overlay analyses of spatial and demographic data from federal and local sources to identify potential human and economic impacts of flooding and 2) create visualization products that show results in a format that emergency responders and decision-makers can easily understand. It covers using data from the 2010 Census and the American Community Survey. Users who are familiar with the 2000 Census data but not the 2010 data will benefit from learning about changes that have occurred. This presentation includes examples of 2-D and 3-D maps created using ArcGIS 10.
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2012 Emergency Track, Emergency Preparedness: Using Local and Federal Data and ArcGIS to Analyze Potential Human and Economic Impacts of Flooding, Valerie Johnson
1. Emergency Preparedness:
Using Local and Federal Data and ArcGIS to
Analyze Potential Human and Economic
Impacts of Flooding
Valerie Johnson, johnsonv@reno.gov, Sept. 21, 2012
Pennsylvania State University MGIS Project
Advisor: Karen Schuckman
Reno-Tahoe Airport, 1997 Flood Downtown Reno, 2005 Flood
Photo Source: Truckee River Flood Management Project
1
2. Outline
What This Presentation Covers
Brief Background of Flooding in Reno, Nevada
Project Goals and Information for Staff
Examples of Visualization Products
Methodology and Data
Spatial Datasets
Property Building Values
Online American FactFinder for Downloading
Demographic Data from the 2010 Census and
the American Community Survey (ACS) for
Census Tracts
Special Steps in Excel
Resources About Census Data
2
3. This presentation covers how
GIS professionals can:
Perform overlay analyses of spatial and
demographic data from federal and local data
sources to identify potential human and economic
impacts of flooding (or other emergency).
Obtain and prep data from the 2010 Census and
the American Community Survey.
Create visualization products that show the results
in a format that emergency responders and
decision-makers can easily understand. Maps,
charts, and tables are well-suited for conveying
such information in a short, targeted report.
3
4. Truckee River Flooding
The Truckee River flows
from Lake Tahoe in
California and through the
hearts of the adjacent cities
of Reno and Sparks in
Nevada, before it ends in
Pyramid Lake.
The Truckee River has a
significant damaging flood
event about every 10 years.
117-year flood in 1997
caused damages of
$650 - $700 million.
50-year flood in 2005 Downtown Reno, 1907 Flood.
caused damages of Bridge, built in 1905, is still in use.
$18 million. Photo Source: Truckee River Flood Management Project
4
5. Area of Interest
East of City of Sparks,
a narrow canyon
constricts the river
Truckee River
5
6. Project Goals -- Info for Emergency
Response Staff …
Identify facilities and populations that may at
risk and require special public safety response
(elderly, very young, limited resources)
Important facilities (schools & colleges, day care, Local
medical care, hotels, government buildings, fire Data
stations, police stations, etc.)
Population (total; under 5 yrs; over 65 yrs)
Population with disability – Unfortunately, data are
currently unavailable at the Tract level Census
Household income (median; household income Bureau
under $15,000/yr) Data
Transportation (households without a vehicle)
Your community may want other categories
6
7. … and for Decision-Makers
Identify city’s current building values and
property taxes for parcels in flood extents
(financial impact of damages)
Buildings that could be damaged by a flood Local
(not condos on 2nd and higher floors) Property
Appraiser/
Assessed values of buildings
Assessor
Net property taxes for entity Data
7
13. Example – Snapshot of Numbers
(Numbers in Table and on Maps are Maximums – See Caveat Later)
Total Population: 63,869
Population 5 and Under: 3,651
Population 65 and Older: 9,493
Population 85 and Older: 1,122
Households With No Vehicle: 4,145
Households With Income $15,000 and Less: 4,036
Building Values in 1997 Flood Extent:
Assessed: $284,504,502
Net Tax Reno: $9,735,535
Building Values in 2005 Flood Extent:
Assessed: $182,845,258
Net Tax Reno: $5,081,778
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14. Methodology and Data
1. Acquire spatial data and re-project as needed.
2. Perform overlay analyses (select by location) to select:
A. Census Tracts intersecting city limits polygon and the 1997
flood extent (1997 and 2005 extents = same selection)
B. Important facilities intersecting combined flood extent.
C. Parcels intersecting each flood extent.
3. Download CSV files of Census 2010 and American
Community Survey (ACS) data. Review and manipulate
tables in Excel. (This is time-consuming!)
4. Use ArcGIS to join Excel file to the Tracts shapefile.
5. Use ArcGIS to create maps. Use Excel to create charts and
tables. Get feedback from staff about what they want to see.
6. Produce short, targeted report. Maintain it!
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15. Spatial Data Spatial Data
Used in Analysis Used Only on Maps
Business data (2010 Hydrographic data
InfoUSA point data) (river, lakes, and creeks)
Census Tracts (ACS data Street centerlines &
is only at Tract level, not major roads
Block Group or Block)
City limits
Flood extents from 1997
and 2005 events Your community may want
Government buildings other features
Medical care facilities
(hospitals, nursing homes)
Parcels with building values
Schools, colleges, day care
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16. Spatial Data
Acquire data from local and federal agencies.
Check the coordinate system of spatial data
and re-project as needed.
You’ll need the Census Tract polygons because the
American Community Survey (ACS) data is available
down to the Tract level (not Block Groups or Blocks).
Local or state GIS Clearinghouses probably have the
Tract polygons. If not, download a shapefile of the
2010 Tracts from:
http://www.census.gov/geo/www/tiger/
The Census Bureau also has a shapefile that includes
some demographic info from the SF-1 form
(population, age, race).
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18. Select by Location … and Caveat
Use Select by Location to get Tracts that intersect the flood
extent polygon. Caveat – Boundaries of Tracts don’t
coincide with boundaries of flood extents, so the count of
people/households “in” the flood extent will be larger than
reality (they’ll be the maximum scenario).
Why? “Select by Location” will Beware - Selected polygons are
select the entire Tract polygons shown with magenta outline.
(black outline) that intersect the Unwanted polygons like 31.01 may
flood polygons. be selected, so check results!
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19. About Differences Between the
2000 Census and the 2010 Census
The 2000 Census included a short-form questionnaire
(data tables SF-1 & SF-2) and a long-form
questionnaire (data tables SF-3 & SF-4).
Starting with 2010, the decennial Census now includes
only the short-form questionnaire, covering topics like
population, age, and race.
Form long-form info like marital status, income, number
of vehicles, and disability* are covered in the more
frequently conducted ACS (smaller sample size).
See “Resources” for links to useful documents,
especially discussions about ACS Margin of Error (+/-).
* Disability data from ACS 5-year estimates slated to be available after 2012.
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20. Obtaining Demographic Data
Use Census Bureau’s
American FactFinder. Go
to factfinder2.census.gov
Under “Geographies”,
pick “Census Tract”
1
Then choose your state,
county, and “All Census
Tracts within County”
Click “Add to Your
2
Selections”
Then close the pop-up
window
20
21. Demographic Data (continued)
Can narrow search by typing in a topic (e.g., Income)
or type in a specific table number.
The next slide lists the table numbers I found useful.
21
22. Census Table Numbers Used for Reno
QT_P1 (“Age Groups and Sex: 2010”, 2010 SF1)
S1901 (“Income in Past 12 Months”,
2010 ACS 5-year estimates)
B08201 (“Household Size by Vehicles Available”,
2010 ACS 5-year estimates)
3
1
2
22
23. Preview Table Before Downloading
If the table has
the info you want,
download it.
Preview of B08201 – Number of Vehicles
23
24. Download
CSV File
Download CSV
1
(zipped file).
“In a Single File” is
fine.
In Excel, you will
have to rename
column headings,
so if you think you
will want to refer to
original column
headings, then 2
choose “Separate
Files”.
24
25. Prep CSV Tables in Excel
First, save CSV file as an Excel file. Use
a meaningful file name; keep table name in it.
Change table – Rename headings in first row, delete
blank & unneeded rows, maybe delete unneeded
columns, and change field types
Table B08201 – Number of Vehicles – in Excel
25
26. Prep CSV Tables in Excel (continued)
Change table – Rename headings, delete blank &
unneeded rows, maybe delete unneeded columns,
and change field types (see next slide)
Could name this GEOID Include “ACS” or Rename field
instead of ID2. “2010” referring to headings (short
source. and meaningful).
In this field, use “Find and Replace” to remove
unwanted text, leaving only the Tract number,
for labeling polygons on a map.
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27. Change ID Field Types in Excel
In order to join tables in
ArcMap, must change the
field containing unique tract
number (“ID2”) from a
number field to a text field.
“Format Cells” to Text type
will not work!
Instead, select a column,
then go to “Data > Text to
Columns”. Choose
“Delimited”, then click
“Next”. Choose “Tab”, then
click “Next”. Choose “Text”,
then click “Finish”.
27
28. Join Tracts Shapefile With Excel Table
Add Tracts polygon shapefile and
Excel table to ArcMap.
Right-click on the Tracts layer and
choose Join.
Unique field with Tract numbers
in the 2010 Tracts layer
is called GEOID10.
Field in table to join is 2nd field
(name depends on what you
named it).
Keep matching records.
Export to new shapefile.
Remove Join. Repeat as needed.
28
29. Visualize Data
Make maps, charts, and tables
that emergency response staff
will find useful.
For map symbology, choose
Quantities > Graduated Colors.
For Fields > Value, choose
category you want to show.
For classification, start with
default -- Natural Breaks
(Jenks). Then click Classify to
adjust “Break Values” to ones
easily recognized.
Get staff feedback on drafts.
29
30. Resources About Census Data
Census Handbook “A Compass for Understanding and
Using American Community Survey Data – What State and
Local Governments Need to Know”:
http://www.census.gov/acs/www/guidance_for_data_users/handbooks/
Short ESRI Slideshow about differences between decennial
census and ACS, as well as Margin of Error:
http://www.slideshare.net/CCIMTECH/esri-2010-census-and-acs
Slideshow produced by Tufts University GIS Center about
using Census’s American FactFinder website and
downloading data, as well as changing headers and rows
of the downloaded CVS tables in Excel:
https://wikis.uit.tufts.edu/confluence/display/GISatTufts/Tufts+GIS+TipS
heets+ArcGIS10 (under “Census Data”, click link to “Census Tutorial:
Downloading and Mapping American FactFinder Data …”
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31. What’s Next For This Project?
Create a short, targeted report.
Check back in a few months for ACS 5-year
estimates about population with a disability.
Keep data tables, maps and report updated as
new ACS data becomes available.
Downtown Reno, Normal Early Summer River Flow
Photo Source: Truckee River Flood Management Project
31