Dictionary

Layer

Source

Description

Aerial Photography

H-GAC

Rectified digital aerial photographs of the Houston-Galveston Area Council. Photographs were taken in January of 2006.

City of Houston Corporate Limit

City of Houston

City limit boundary of the City of Houston. Downloaded from the City of Houston website http://www.gims.houstontx.gov on September 22, 2006

Attributes
Square Miles Contained Within City Limits

Conveyance Zones

TCB

Conveyance zones were determined to comply with Chapter 19 of the City of Houston Ordinance. They define areas that are likely to have overland flow as part of the floodplain. In conveyance areas, the City requires a conveyance analysis to ensure that development will not reduce the conveyance of the floodplain. Conveyance areas were determined as areas that meet one or more of the following conditions:

within the floodway
within the floodway buffer (defined as the area within 100' of the floodway boundary)
between channel centerlines in an overflow area (in or near an AO zone)
natural ground elevation greater than 18" below the base flood elevation (BFE)

Because of the vertical accuracy of the LiDAR elevations used to determine natural ground elevations, the calculations used to determine conveyance zones selected areas greater than 15" below the BFE. Where depth is the reason an area is in the conveyance zone, a surveyed elevation should be compared to the BFE to determine the actual depth and more accurately place any given location inside or outside the conveyance zone. Conveyance analysis will not be required where survey indicates that the depth is less than 18", except that it is always required where the conveyance zone is within the floodway or the floodway buffer.

A raster-based analysis was used as part of the procedure to develop the conveyance zones, so the boundaries do no exactly match the TSARP floodplain boundaries. Horizontal accuracy should be within 15 ft.

Attributes

Conveyance

Values include: “Yes: Floodway or Buffer or Overflow” to indicate that the area is within one of these three areas. Permit applications in these areas should have conveyance analyses; “Yes: Depth” to indicate that the area is in the conveyance zone because of depth. These areas may not require a conveyance analysis if the elevation survey indicates that the area is less than 18" below BFE; “No” or “No: Disconnected” to indicate that the area is less than 15" below BFE or is disconnected from the floodway. Site survey should be checked to confirm the depths; and “Not Analyzed” to indicate that the area was outside the HEC-RAS model boundary and that site survey should be used to determine if it is within a conveyance zone.

Council Districts

City of Houston

Council District boundaries for the City of Houston. Downloaded from the City of Houston website http://www.gims.houstontx.gov on September 22, 2006

Attributes
Council District
Council Member Name
Square Miles in Council District

Counties

TWDB

County boundaries of Texas Counties as digitized for the Texas Strategic Mapping Program (StratMap). Data is dated September 20, 2001.

Attributes
County Name

Effective FIRM (TSARP) BFE

HCFCD

Base Flood Elevation lines created as part of the Digital Firm Mapping project for Harris County conducted post Tropical Storm Allison. Distributed by the Harris County Flood Control District, June 9, 2006 revision.

Attributes
Base Flood Elevation	Elevations NAVD 1988, 2001 adjustment

Effective FIRM (TSARP) Floodplains

HCFCD

Effective boundaries of the Floodway, 100 year floodplain and 500 year floodplain in Harris County created as part of the Digital Firm Mapping Project for Harris County conducted post Tropical Storm Allison. Distributed by the Harris County Flood Control District and FEMA. These boundaries became the effective boundaries on June 18, 2007.

Attributes
Flood Zone	Values include “Floodway”; “AE” for 100 Year - base flood elevation determined; “AO” for 100 Year - flood depths 1-3 feet, average depths determined; “A” for 100 Year - base flood elevation not determined; “VE” for Coastal flood zone - base flood elevation determined;and “0.2 Pct Annual Chance” for 500 Year.

Effective FIRM (TSARP) Watersheds

HCFCD

Major Watershed boundaries in Harris County. Distributed by the Harris County Flood Control District. The version shown was acquired in October 2003.

Attributes
Name
Unit Name

Existing Storm Sewer Pipe

TCB

Existing storm sewer pipes compiled for and used in developing the City of Houston Comprehensive Drainage Plan. The original data was published in 1999. Kingwood data was added in 2001 and data for previously unstudied areas was added in 2003.
This storm sewer data has not been updated to reflect changes since the CDP was developed. For the most current information about the existing storm sewer system, please visit the City of Houston Public Works and Engineering Department's GIMS system.

Attributes
Line Type
Rise	Diameter of round pipes, height of box or elliptical pipes
Span	0 for round pipes, width of box or elliptical pipes
Material
Upstream Elevation
Downstream Elevation
Outfall Name
Design Flow
Existing Capacity

FIRM Panels

FEMA, TCB

FIRM Panel boundaries from FEMA associated with the Effective FIRM (TSARP) Floodplain. Attribute data has been modified to include LOMR case numbers for areas affected by LOMRS that fall within the associated FIRM Panels. These case numbers are added by TCB as they are supplied to the City of Houston by FEMA.

Attributes
FIRM Panel	FEMA designated FIRM Panel number.
LOMR Case Number	List of LOMR Case Numbers for areas affected by LOMRS that fall within the FIRM Panel.

Flood Survey Respondents

TCB

Location of street or house flooding based on the drainage survey sent to City of Houston residents, as described here. Only responses showing at least 1 occurrence of street flooding, streets impassable due to high water, or house flooding are shown. The location was established by address matching the supplied address to the US Census Bureau”s tiger files.

Attributes
Flood Insurance	1 = Resident had flood insurance at the time of the survey; 0 = Resident did not have flood insurance at the time of the survey

Flow Paths

TCB

Overland flow paths draining areas of various sizes. Obtained by performing a hydrologic analysis on the 2001 LIDAR data. These flow paths may not represent true direction of flow in areas where buildings or roads obstructed LIDAR data collection.

Attributes
Drainage Size	Minimum area to begin showing flow path and represent overland flow assuming that storm sewers are absent or the rainfall is above the designed capacity of the storm sewer.

LOMC

TCB

Boundaries of areas impacted by changes to the Effective Flood Insurance Maps. Changes are approved by FEMA and issued as letter of map changes (LOMC). This layer was last updated on 8/5/2008.

Attributes
Case Number	FEMA designated Case Number. Clicking on this attribute will initiate a hyperlink that will display a scanned copy of FEMA's LOMC. For the hyperlink to function properly, Adobe Acrobat Reader must be installed on the computer.
Community	FEMA designated community affected by the LOMC.
Effective Date	The date the LOMC became effective.
Issue Date	The date the LOMC was issued by FEMA.
Affected Panels	List of FEMA FIRM panels that are affected by the LOMC.
Identifier	Name or identifier associated with the LOMC.
Project Description	Description of the project type. Current values include: Channelization, Fill, FW Removal, No Project, and Removal
Basis of Request	Brief description of the basis of the request.
Type	Type of LOMC document. Current values include: LOMA, LOMR-APP, LOMR-F, and LOMR-FW

Major Roads

City of Houston

Major roads and freeways in the City of Houston area. Distributed by the City of Houston Planning Department as part of COHGIS 10.

Attributes
Name

Major Waterways

City of Houston

Major water features in the Houston area. Distributed by the City of Houston Planning Department as part of COHGIS 10.

Attributes
Name

Manhole

TCB

Manholes compiled for the City of Houston Comprehensive Drainage Plan.
Elevations are on a number of different vertical datums and typically represent elevations taken from construction drawings.

Attributes
Manhole Type
Rim Elevation
Flow Elevation
Outfall Name

Overland Drainage Areas

TCB

Drainage areas determined for overland flow from the 2001 LIDAR data, assuming that storm sewers were absent or that the rainfall is above the designed capacity of the storm sewers.

Attributes
Drainage Channel
Drainage Area Name
Total Count
Survey Flooded Structures
Repetitive Loss Structures
Drainage Area (acres)

Pavement Edge

City of Houston

Edge of pavement in the City of Houston area. Distributed by the City of Houston Planning Department as part of COHGIS 10.

Parcels

COH, HCAD

Parcel boundaries from the City of Houston, COHGIS 12 dataset. The attribute data was downloaded from the HCAD website http://pdata.hcad.org/GIS/index.html in June 2006 and linked to the parcel boundaries.

Attributes
Account Number	HCAD account number
Tax Year
Site Address	Physical address of the property
Key Map	Key Map grid the property is in
Owner	The first listed owner according to HCAD
Owner Address	Mailing address of the owner
Land Value	Assessed value of the land
Improvements Value	Assessed value of the property improvements
Extra Features Value
New Owner Date
Legal Description

Ponding

TCB

Ponding areas associated with the overland drainage analysis. These areas do not represent actual ponding from a given storm, but the minimum depth of ponding required to produce overland flow when a storm sewer is absent or rainfall is above the storm sewer's designed capacity. Based on the 2001 LIDAR data.

Previous FIRM Floodplain

FEMA

Boundaries of the Floodway, 100 year floodplain and 500 year floodplain in Harris County digitized from FEMA”s effective firm panel maps prior to Tropical Storm Allison.

Attributes
Flood Zone	Values include “FW” for Floodway; “A” and “AE” for 100 year floodplain; and “X5” for 500 year floodplain.

Proposed New Storm Sewer

TCB

Storm sewer trunks for proposed storm sewer pipes compiled for the Comprehensive Drainage Plan in undeveloped areas or areas with roadside ditches. A full system was not designed to the inlet level.

Attributes
Line Type
Rise	Diameter of the pipe
Outfall Name
Length	Length of the pipe in feet

Proposed Storm Sewer Upgrades

TCB

Storm sewer pipes recommended to be upgraded in size. Extracted from the storm sewer layer complied for the City of Houston Comprehensive Drainage Plan.
Elevations are on a number of different vertical datums and typically represent elevations taken from construction drawings.

Attributes
Line Type
Proposed Size for 2 Year Flood
Existing Rise	Diameter of round pipes, height of box or elliptical pipes
Existing Span	0 for round pipes, width of box or elliptical pipes
Material
Upstream Elevation
Downstream Elevation
Outfall Name	Comprehensive Drainage Plan outfall in which pipe falls
Cost	Estimated cost to upgrade the pipe

Storm Sewer System Drainage Area

TCB

Drainage area boundaries for storm sewers in the City of Houston Comprehensive Drainage Plan. These drainage areas are sometimes referred to as Outfalls or CDP Outfalls.

Attributes
Capacity for 2 Year Flood
Improvement Cost for 2 Year Flood
Number of Homes on this Outfall System
Improvement Cost per Address for 2 Year Flood
Number of Street Flooded Complaints for this Outfall System
Number of Flooded Houses in this Outfall System

Stormwater CIP

City of Houston

Boundaries of approved City of Houston Stormwater Projects for City of Houston fiscal year 2007.

Attributes
CIP Number
Project Name

Streets

H-GAC

STAR*Map streets created and maintained by the Houston-Galveston Area Council. The version on this website is from March 30, 2006.

Attributes
Range Lower Left
Range Lower Right
Range Upper Left
Range Upper Right
Prefix
Name
Street Type
Suffix

Subdivisions

City of Houston

Subdivision boundaries in the Houston Area. Downloaded from the City of Houston website http://www.gims.houstontx.gov on September 22, 2006

Attributes
Subdivision	Subdivision Name

Waste Water Lines

City of Houston

Existing waste water line features in the City of Houston. Provided by the City of Houston Geographic Information Management System in June 2007

Attributes
Upstream Elevation
Downstream Elevation
Span	Diameter of round pipe, width of box or elliptical pipe
Rise	0 for round pipe, height of box or elliptical pipe
Line Type

Water Lines

City of Houston

Existing water line features in the City of Houston. Provided by the City of Houston Geographic Information Management System in June 2007

Attributes
Privately Owned
Line Type

Waterway

HCFCD

Channel centerlines for water features in Harris County. Distributed by the Harris County Flood Control District. The version shown was acquired in November 2006.

Attributes
HCFCD Unit Number
Common Name

2 ft Contours

HCFCD

2 foot contour lines for the City of Houston. Extracted form 2 foot contour lines created for the Harris County Flood Control District from LIDAR data obtained in October and November of 2001.

Attributes
Elevation	Elevations NAVD 1988, 2001 adjustment