A command used to retrieve information from a database

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4
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2answers
2k views

Postgis, get the points that are x meters near another point, in meters

I'm trying to find the points within a certain distance, in meters, from another point. I'm using the function ST_Buffer, but I don't get how to express the distance in meters. I'm trying with ...
3
votes
4answers
5k views

How to group and count attribute data?

I have a problem with group same data to count it. For example, i want to group same code to one and count them. I can do it when i use MapInfo (Pic 1) but i can't in QGIS. (Pic 2: i can classify ...
2
votes
2answers
3k views

Merge lines with the same 'name' attribute on QGIS?

I have a shapefile with a few thousand lines, each is a street segment. I'd like to merge all features with the same 'streetName' attribute into a single attribute. I only really care about the name ...
1
vote
2answers
1k views

ST_DWithin uses Geometry or Geography type

assuming I use the following query to match the locations to a poi within 10km distance: SELECT poi.poi_id, h.loc_id, (ST_Distance(poi.geom,h.geom)*111.111) as distanceinkm FROM iut_poi_transl AS poi,...
15
votes
3answers
12k views

Idiots guide to expressions for QGIS

I have no formal training in GIS and have learned on the fly with ArcGIS 9.3 at work and have been dabbling with QGIS on my own time for my business. Is there any resource recommendations ingeneral ...
6
votes
1answer
3k views

How do I perform a proximity search with Postgis?

OK, so I downloaded the Geonames database (cities1000) and wrote a small Ruby program to import them into my table (geo_cities). I then added geography column called geog. So after all of that, I ...
1
vote
1answer
1k views

SQL Server Spatial Querying

I am looking for ways to learn querying for SQL Server Spatial (2008/2012). I have a table created from Shape2SQL and have been trying to run a simple intersection query to get results from that ...
5
votes
1answer
222 views

How to build a query/expression to select specific points within a buffer? (in QGIS)

I have a point layer in QGIS. Each point represents a tree and each tree has information about its height as an attribute. I would like to build a query/expression to select all those trees that have ...
4
votes
1answer
8k views

How to filter features in a layer?

I am trying to display certain features in a shapefile-based layer using QGIS. I have found the subset function in the properties panel, which does exactly what i want, but is too tedious given that I ...
2
votes
1answer
1k views

Why does my PostGIS query fail with “current transaction is aborted”

I'm trying to create a vector layer in a QGIS project using a PostGIS query. QGIS is returning the following error: Query failed 1 cursor states lost. SQL: CLOSE qgisf1 Result: 7 (ERROR: ...
2
votes
4answers
776 views

PostGIS doesn't use spatial index with ST_Intersects

I imported the data from openstreetmap using osm2pgsql and copied it another table structure. If I made a query for containing rows using st_intersects, st_contain or someone else, postgis don't use ...
1
vote
2answers
843 views

How can I calculate how many of a certain feature lie within my various buffer rings?

I am using ArcMap and I have a series of real estate parcels mapped along with a series of wind turbines. I have created multiple buffer rings around each real estate parcel with distances (0.5, 1, 1....
1
vote
2answers
1k views

Searching planet_osm_point by longitude and latitude

I used osm2pgsql to import data into my PostgreSQL database and it put gave me the following 4 tables, planet_osm_point, planet_osm_line, planet_osm_polygon and planet_osm_roads. I have looked at ...
1
vote
2answers
90 views

SQL query new feature with loop

I'm trying to create an individual buffer feature class for each column of an input feature class, where there is a field that contains the buffer distance. I think there is a problem with my SQL ...
0
votes
2answers
119 views

How to implement a radius search using PostGIS

I am very new to this topic and after a long time of research I didn't find a solution. I want a query that I can use on my PostGIS database performing a radiussearch.. I inserted the Open Street Map ...
28
votes
3answers
2k views

Is there a “Select by Attributes” plugin/widget for ArcGIS Server JS API?

I'm hoping to find some existing code which emulates the "Select by Attributes" dialog in ArcMap, within the ArcGIS Server JavaScript API. Writing a hard-coded QueryTask is easy - I'm looking for ...
12
votes
3answers
2k views

How to speed up queries for raster databases?

I have a raster database in postgresql/postgis with these columns: (ID, rast, data_of_data). 'rast' is the column that has raster files in WKT format. An example query to find the DN value of a ...
20
votes
2answers
7k views

How to select features with NULL attributes in QGIS?

I need to identify which features have null attributes in the attribute table of a shapefile. When i try [field]= 'NULL' it selects the features with value=0 (see picture) Suggestions?
15
votes
1answer
496 views

How to query OSM for all beaches facing west? - QGIS preferred

I want to identify all beaches on this planet (or a given subset of it) that are facing westwards (+/- 20-30 degrees). My idea is to use OSM as the data source. Extracting all polygons that have the ...
13
votes
6answers
5k views

Identifying duplicate attributes in field using QGIS?

I have a point shapefile with thousands of points. It has an ID code field that is supposed to be unique. Every now and then the data entry clerk wrongly type the ID creating duplicates. Right now I'm ...
8
votes
2answers
279 views

Find headwater polygons

This is a follow up question to this question. I have a river network (multiline) and some drainage polygons (see picture below). My goal is to select only the headwater polygons (green). With ...
6
votes
3answers
6k views

How to fix performance problem in PostGIS ST_Intersects?

I'm a newbie in postgis and I have a problem in query performance. This my query: SELECT DISTINCT ON (userid) userid ,ST_AsText(position), timestamp FROM table1 WHERE ST_Intersects ( ...
4
votes
3answers
3k views

Selecting MAX values within records with the same name

I'm working in ArcMap 9.3 and I've never dealt with that kind of queries... I need to Select the MAX value from column [A] for each set of records in the table which have the same value in column [B] ...
2
votes
1answer
580 views

How to apply a filter to multiple vector layers in QGIS?

I am trying to apply an attribute filter to multiple layers in QGIS at once. The filter is to be applied to .osm data brought in through PostGIS to QGIS. I have tried selecting multiple layers -> ...
1
vote
1answer
1k views

How to query all layers in ArcMap and get access to them by name or index?

I have ArcMap with tons of layers. Some of these layers may contain another layers with data (aka Composite layers) or they don't. The depth of composite layers in unknown. I need to query all layer ...
7
votes
2answers
2k views

How do I use QGIS python console to iterate through simple layer queries and png outputs?

I'm really new to QGIS coding and I'm having a hard time finding (especially) the api classes/functions to carry out actions of the Query Builder window. I'm basically trying to do this: Iterate ...
6
votes
1answer
811 views

Need to learn more about Precision and Accuracy

I am currently taking Introduction to Image Interpretation online and there is a section in it that talks about Precision and Accuracy. I wanted to know if someone out there has any good information ...
4
votes
2answers
1k views

Spatial query of raster data

I have population distribution data as a raster layer and exposure contours as vector (polygon) layers. What I'd like to do is use the vector layer to estimate the population indicated from the raster ...
3
votes
0answers
624 views

How do I determine appropriate Date query syntax for a layer?

I'm writing a web mapping query tool to query Esri mapservice layers by date using the REST API. It has been said that the syntax depends on what kind of database is behind the mapservice layer, as ...
3
votes
1answer
445 views

PostGIS - ST_Within or ST_Disjoint performance issues

I have a table of about 150,000 points in PostGIS with a spatial index and a SRID of 27700 (OS). I want to select the points that fall outside England and Wales. I have a multipolygon table with ...
3
votes
2answers
631 views

How fill length and feature count in PostGIS table for each polygons

I'am new to PostGIS/PostgreSql. I have a database which containts two shape-files : polygonal layer towns and linear layer of roads To calculate the length and feature count of 'Streets' inside ...
1
vote
2answers
92 views

How to add state polygon information to a city point?

I have the following layers: Country border federal state borders cities (located as points) I would need the following result file (txt or csv..): A column with the name of the city and another ...
0
votes
1answer
3k views

Query Feature using OpenLayers + MapServer

I'm trying to query a feature in OpenLayers, but it's returning just an image highlighted that is not possible to make zoom, pan and drag. My intention is to query a feature on the map like street ...
6
votes
2answers
539 views

Find start of river

Edit: Follow-up question here (= Find headwater polygons). How can I determine the start of a river in PostGIS? I have a river network (Multiline) and want to find the startpoints of the rivers. ...
4
votes
2answers
1k views

What is the best approach to using IQueryFilter.WhereClause in ArcObjects?

What is your preferred / best approach to using IQueryFilter.WhereClause statements in ArcObjects (e.g. when selecting features by attributes)? You need to check the source type (shapefile / personal ...
3
votes
1answer
930 views

query / filter on attribute tables with external tables joined

i tried to do some queries on joiend table fields ... i've got/found some answers concerning version 1.8 - which result in "use select + export to create a combined dataset" so i just did some tests ...
3
votes
1answer
354 views

Filter contour lines in QGIS

I have a shapefile of contour lines, with an ALTITUDE attribute with the height ASL in metres. The source data is in 0.5m intervals, but I'd like to filter it down so I get contour lines at (for eg.) ...
3
votes
1answer
217 views

Selecting limited TOP n from specific column in ArcGIS query builder?

I'd like to know what is the best way to select a limited top 'n' of rows from a specific column of a geodatabase file. Currently I use a function in the query builder of the select tool (arcgis10) in ...
3
votes
1answer
145 views

Cemetery Grave/Person Locator

I'm a mediocre to intermediate ArcGIS user. I have created several point shapefiles, one for each section of a national cemetery, roughly 200-600 points in each section in a grid. Attached to these ...
3
votes
2answers
1k views

Why does ArcGIS Server not return data when querying joined fields?

I've been trying to help troubleshoot an issue that is very strange, and I think we've boiled it down to an issue with ArcGIS Server. We have a map service that shows up in the services directory as: ...
2
votes
1answer
4k views

Basic MapServer query of PostgreSQL/PostGIS database

I've just installed MapServer on a linux server and I am trying to understand how to display a basic map using a PostGIS database. I have displayed a shapefile in the browser, so I know that the ...
0
votes
1answer
31 views

OSM: Getting the correct Overpass Turbo query using a keyword (and values)

I'm completely new to Overpass queries for getting OSM data, so sorry for this maybe trivial question. I'm looking for the correct query using Overpass turbo. I have found some demo queries, but I am ...
0
votes
0answers
288 views

ArcMap ObjectID seems to be getting changed, any ideas what might be doing it?

I am working with ArcMap10.0 and MDB's, often creating Definition Queries based off my ObjectID with the understanding that this unique identifier should not change over time. ie. if I create ...
0
votes
1answer
1k views

SQL Geometry Query similar to Select by Centroid

Does anyone know if it's possible to query SQL geometry by something like 'centroid of polygon'...similar to ArcMap's select by location? I'm using SQL Server 2008 R2 as the DBMS. I have two polygon ...
0
votes
3answers
129 views

Pass GeoJSON from .NET to Javascript

My .NET/OpenLayers/GeoServer/PostGres-PostGIS application allows users to create custom queries to get data from my PostGIS tables. The queries are called in .NET (not javascript) using a web method ...