DOI: 10.7910/dvn/75ji3a
title: Bathymetry Points, Lake Victoria, vector points, 1900 - 2017, V7

description: &lt;font size = "5"&gt;&lt;b&gt;Bathymetry Points, Lake Victoria, vector point, 1900-2017&lt;/b&gt;&lt;/font&gt;
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&lt;b&gt;&lt;u&gt;Reference Information and Units:&lt;/u&gt;&lt;/b&gt;
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Projected Coordinate System: Africa Lambert Conformal Conic
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 ESRI:102024 (https://epsg.io/102024)
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 GCS: GCS_WGS_1984
 
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&lt;b&gt;&lt;u&gt;File Naming Convention:&lt;/u&gt;&lt;/b&gt;
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LV_Bathymetry_Points_V7.shp
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&lt;b&gt;&lt;u&gt;Data Origin:&lt;/u&gt;&lt;/b&gt;
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Admiral Bathymetric Maps:
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 Description: British admiral bathymetry maps of the lake. Maps were scanned and georeferenced. Once georeferenced the depth points were digitized
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 Points: Approximately 5,212 
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 Year: 1900-1955
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Depth Sounder: 
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 Description: Depth readings taken from a depth sounder were read into ArcMap using X, Y coordinates
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 Points: Approximately 5,888
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 Year: 2013
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German Bathymetry Map:
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 Description: A German bathymetry map was scanned and georeferenced. Once georeferenced the depth points were digitized.
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 Points: Approximately 50
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 Year: 1913
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Acoustic Surveys from Nafirri:
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 Description: Instruments used are two Depth Profiling systems (a submersible Conductivity Temperature-Depth profiling system (CTD, Sea and Sun Technologies) 
 and a YSI 650 multiparameter Sonde). Readings were read into ArcMap using X, Y coordinates.
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 Date: 11/2015: 
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 Approximately 55 points
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 Date: 8/2016
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 Approximately 50 points
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Limnology Survey from Nafirri:
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 Description: Limnology survey using acoustic equipment and GPS
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 Points: Approximately 10
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 Date: 2007/2008

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Sounding Data:
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Description: Depth readings taken from a depth sounder were read into ArcMap using X, Y coordinates
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Points: Approximately 17,200
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Date: 2009
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Acoustic Sounder Strata Data:
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Description: Points were taken to determine the strata of the lake by using a Simrad EK60 echo sounder.
These points contained Z values. The points were read into ArcMap using X, Y coordinates
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Points: Approximately 45
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Date: 2009
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Lake Victoria Bathymetric Survey For EAC/LVBC:
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Description: Points were taken using a single beam echo sounder 200kHz and were provided from Ola at MMT. These points are concentrated in three bays, Mwanza Gulf (TZ), Kisumu (KY), and Port Bell (UG).
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Points: Approximately 120,000
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Date: 2007
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Lake Victoria Regional Hydro-acoustics Working Group:
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Description: The survey was conducted by the Lake Victoria Regional Hydroacoustics Working Group under coordination of LVFO with NSF project funds. It was conducted using Tanzania's RV. Lake Victoria Explorer. 
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Points: Approximately 3,945,260 
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Date: 09/12/2017 – 10/5/2017
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&lt;b&gt;&lt;u&gt;Data Development:&lt;/u&gt;&lt;/b&gt;
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The final bathymetry points were created by converting all sources to the same unit(meters). Once all sources were in the same unit they were combined into the same file. When all points were in the same file a spatial query was ran to select all the bathymetry points that fell outside of the Lake Victoria shoreline polygon. Any point that was located outside of the shoreline polygon was removed from the file. The next step was to remove the redundant points. PostgresSQL was used to find all the points that were within 100 meters from another point (SQL Code 1). One of the points would be removed from the final set of points to clean up the data. The points that were obtained from the survey conducted for the EAC/LVBC were not included in the removing of points within 100 meters of one another. Any point from version 6 that was located within 100 meters of a point from the Lake Victoria Regional Hydro-acoustics Working Group dataset, was removed. All points from the acoustic survey conducted by Lake Victoria Regional Hydro-acoustics Working Group were kept regardless of their distance from each other. PostgresSQL was also used to check the depths of points in relation to points around them to determine outliers (SQL Code 2). Outliers were double checked and removed if not deemed plausible. Points that were denoted as “greater than” the recorded depth were removed if the depth was less than 60.96 meters. 
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SQL Code 1: Finds all points within 100 meters of another point
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select a.objectid, b.objectid
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from lv_bathymetry_points_v5 as a, lv_bathymetry_points_v5 as b
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where st_distance(a.geom,b.geom) &lt; 100
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and a.objectid != b.objectid
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SQL Code 2: Checks for points with depths that are outliers compared to neighbor points
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select a.objectid, b.objectid, (@(a.z - b.z)) as z_diff
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from lv_bathymetry_points_v5 as a, lv_bathymetry_points_v5 as b
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where (@(a.z - b.z)) &gt; 5
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and st_distance(a.geom, b.geom) &lt; 200
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description: ArcGis, 10.3
description: Please disregard the dataverse version number.