79
votes
22answers
21k views

How to Start Web Mapping?

I want to start working on a web map at work to map some of our statistics by city. I have an idea, but I'm not exactly sure where to start. Are there any definitive resources that provide step ...
27
votes
3answers
27k views

Layers with same coordinate system should align/overlap but do not?

I put 4 different layers into my ArcMap document, but only one of them will show up on the map! I should be seeing the other 3 layers as well. When I do a Zoom to layer, I can see one layer, but I ...
84
votes
5answers
14k views

How do I access ArcObjects from Python?

I would like to be able to script some things that are not exposed via arcgisscripting or ArcPy. How do I access ArcObjects from Python?
73
votes
4answers
48k views

File Geodatabase (*.gdb) support in QGIS?

Following questions: Open Source Tool capable of reading Esri File Geodatabase (.gdb)? How to access file geodatabase in Qgis? How to get FGDB support in GDAL 1.9 without compiling? I have spent ...
35
votes
11answers
15k views

Identifying Coordinate System of Shapefile when Unknown?

I have a Shapefile but its coordinate system is Unknown, and there is no *.prj file. How I can identify it now? Are there any tools that could help?
124
votes
5answers
102k views

How to measure the accuracy of latitude and longitude?

I am very new to GPS stuff. Suppose I have latitude and longitude as 19.0649070739746 and 73.1308670043945 respectively. In this case both coordinates are 13 decimal places long, but sometimes I also ...
8
votes
4answers
8k views

How to fix QGIS error “Entry Point could not be located”?

Today, after returning from vacations, I started my QGIS 1.7 and got this terrible message: Help, anyone?
145
votes
11answers
43k views
37
votes
10answers
11k views

What are some resources for learning ArcPy?

I would like to learn ArcPy, but I do not know quite where to begin. Does anyone have any good advice on where I should start to learn ArcPy?
16
votes
9answers
21k views

Calculating Lat/Lng X miles from point

I am wanting to find a latitude and longitude point given a bearing, a distance, and a starting latitude and longitude. This appears to be the opposite of this question (Distance between lat/long ...
14
votes
3answers
23k views

Converting ArcGIS layer style to Styled Layer Descriptor (SLD) file?

I am putting together a GIS server using GeoServer and need some help with importing my layer styles from ArcGIS 10 to SLD format. I have one layer in ArcMap properly symbolized and labeled, how ...
50
votes
11answers
36k views

How to install GDAL with Python on windows?

Can anyone please explain to me in step by step instructions how to install GDAL/OGR with Python on Windows. I have Windows Vista and I have tried following the information on the website and it does ...
27
votes
12answers
10k views

Different approaches for map matching : links / ideas?

I'm using Open Street Map and its vectorial road network and I'd like to implement a map matcher algorithm. Currently I'm able, for each GPS position, to retrieve the nearest road segment and ...
9
votes
3answers
8k views

How to include variable in where clause of arcpy.Select_analysis?

I am trying to loop through a shapefile, selecting each feature in turn and copying it to a temporary shapefile to by included in a union analysis. I'm using a cursor to find the ID name for each ...
23
votes
6answers
10k views

Shapefile PRJ to PostGIS SRID lookup table?

I was wondering if there is such a thing as an shapefile PRJ to PostGIS SRID lookup table? Something that can translate the most standard shapefile PRJ definitions into the likely SRID. When using ...
73
votes
14answers
24k views

What are Definition, Algorithms and Practical Solutions for Concave Hull?

Convex Hull A convex hull of a shape is defined as: In mathematics, the convex hull or convex envelope for a set of points X in a real vector space V is the minimal convex set containing X ...
32
votes
4answers
4k views

Performance of ArcGISScripting and large spatial data sets

I am currently writing a python script using the arcgisscripting module to process a reasonably large data set (~10,000 records in total) normalised over a small number of tables, 8 in total. The ...
21
votes
1answer
2k views

What is most accurate coordinate system for calculating areas of polygons?

I have multiple polygons, all located offshore around the UK. I am trying to calculate the areas of these polygons in square kilometres, without splitting them by UTM zone. Is it possible to do this ...
9
votes
4answers
7k views

How to use SRTM Global DEM for Slope calculation?

I have downloaded SRTM GDEM (~90 km resolution). I am using ArcGIS 10. I have tried to use spatial analyst to compute for slope. However, I can not compute for the slope. The output values has only ...
46
votes
3answers
56k views

Algorithm for offsetting a latitude/longitude by some amount of meters

I'm looking for an algorithm which when given a latitude and longitude pair and a vector translation in meters in Cartesian coordinates (x,y) would give me a new coordinate. Sort of like a reverse ...
24
votes
5answers
31k views

Get list of coordinates for points in a layer?

I've got a layer in QGIS that is comprised of points. Its attribute table doesn't have (show) the corresponding x and y coordinates for each point. Is there a way for me to extract a list of ...
9
votes
5answers
5k views

Why do OpenLayers layers appear shifted in map composer?

I'm having trouble with the OpenLayers Plugin of Qgis and the map composer: If I create an OSM-background layer and if I want to export this, the OSM-Layer looks perfectly all right in the normal ...
138
votes
18answers
53k views

How do various JavaScript mapping libraries compare? [closed]

I am working on a web-based mapping system and I'm trying to figure out the best/most appropriate library to use. There are a few of them about and they each have pros and cons. Even after trying a ...
60
votes
6answers
29k views

How to build effective heat-maps?

Using ArcGIS, QuantumGIS, Grass, and/or GVSIG What are some of the tools and processes involved in building effective heat maps? What are the plugins involved? What are the major data requirements? ...
54
votes
16answers
10k views

Where to find QGIS tutorials and web resources?

I wish to familiarize myself with the capabilities of QGIS. I have downloaded the program, but apart from basic loading of data, I am lost (even after reading the help file). Can you recommend me ...
68
votes
20answers
58k views

How to convert between KML and Esri's shapefile (SHP) format?

My users are sending me point data that were digitized using GoogleEarth. How can I convert their KML to a shapefile?
29
votes
2answers
3k views

How accurate is approximating the Earth as a sphere?

What level of error do I encounter when approximating the earth as a sphere? Specifically, when dealing with the location of points and, for example, the great circle distances between them. Are ...
42
votes
6answers
12k views

Why is the 'straight line' path across continent so curved?

This is the result of mapping the straight line path from a point in US to Poland using Distance Measurement Tool. Also, planes from Asia to US would travel almost over North Pole. Why is the path ...
23
votes
5answers
15k views

What is difference between map layer and spatial dataset (e.g. feature class, shapefile)?

This may be very trivial question. To me they seems very similar in concept. What is the difference between feature class and feature layer?
24
votes
10answers
4k views

What are the existing solutions to automate generalisation/simplification of geographical data?

I am looking for existing solutions (softwares, libraries, methods, etc.) to automate the generalisation/simplification of geographical data as presented there, and also there. How do you proceed ...
47
votes
7answers
4k views

What strategies, criteria, or rules to use for selecting coordinate systems?

What strategies, criteria, or rules do you use for selecting coordinate systems for (a) storing, (b) analyzing, and (c) displaying GIS data? (I humbly offer my reply to a related question ...
26
votes
3answers
16k views

Why is law of cosines more preferable than haversine when calculating distance between two latitude-longitude points?

In fact, when Sinnott published the haversine formula, computational precision was limited. Nowadays, JavaScript (and most modern computers & languages) use IEEE 754 64-bit ...
22
votes
12answers
21k views

Converting Shapefiles to Text (ASCII) files? [duplicate]

How can I convert a shape file (GIS) to text? or, How can I extract the information in a shape file?
23
votes
4answers
4k views

Bulk load multiple shapefiles into PostGIS

I've got over a hundred data layers in shapefile format that I want to upload into a PostGIS database. They are all in the same projection, but represent different data layers so they do not have the ...
27
votes
3answers
25k views

How to clip a raster with vector boundaries?

I am using QGIS. I would like to clip a raster precipitation layer using an admin boundary layer that is vector data. However the geoprocessing tools seem to be usable only for vector data. How can ...
23
votes
1answer
3k views

How to create an accurate Tissot Indicatrix?

A Tissot Indicatrix is useful method for communicating at a glance the kinds of distortion a given projection is prone to (in the figure below, each of the red circles occupies the same area). I've ...
20
votes
1answer
6k views

How to define new custom projections in QGIS?

I'm trying to define a projection in QGIS. I want to add North America Albers Equal Area Conic. From the spatialreference site I copied the proj4 line: +proj=aea +lat_1=20 +lat_2=60 +lat_0=40 ...
9
votes
1answer
625 views

Using customized Coordinate System for Archaeological site data

I don't know so much about coordinate systems... In my office we use to deal with spatial data coming from archaeological sites. Each site has its own x-y-z coordinate system (GCS). Three simple ...
14
votes
5answers
16k views

Changing CSV layer attribute value from text to number in QGIS?

I read in a CSV file for linking to a .shp file. All the variables that are just numbers came in as text. How do I change the text variables to numeric in QGIS?
9
votes
11answers
12k views

Exporting feature class into multiple feature classes based on field values using ArcGIS for Desktop?

I have a feature class with over 2,000 features, and I need to make them all individual feature classes based on a field. I know there has to be a way to do this, but I just can't figure it out! ...
21
votes
10answers
7k views

What are useful websites for scouting GIS related jobs? [closed]

What are useful websites for scouting GIS related jobs?
25
votes
10answers
6k views

Alternatives to pgRouting

I was wondering if there are any alternatives to pgRouting tools. Thinking about it for a bit, I think the only alternative is to use R or RPY to do the analysis. Basically I'm trying to solve ...
23
votes
1answer
10k views

Trilateration algorithm for n amount of points

I need to find algorithm that can calculate centroid A (aka gravity center, geometric center, center of mass) from the figure where circles T1,T2,T3,T4,T5,..,Tn intersect AND length of line R from ...
32
votes
2answers
12k views

What raster smoothing/generalization tools are available?

I have a DEM that I would like to smooth or generalize to remove topographic extremes (chop off peaks and fill-in valleys). Ideally, I would also like to have control over the radius or level of ...
31
votes
7answers
17k views

Most Up-To-Date Source for US Zip Code Boundaries

I was just wondering what the most up-to-date source for US Zip Code boundaries would be. My first thought was TIGER, whenever that comes out, but then I thought that the Postal Service might be a ...
10
votes
8answers
8k views

How to georeference a vector layer with control points?

I have a non-georeferenced vector layer that I need to be georeferenced. With raster layers the task is easy and straightforward, but I have no idea what should I do with my vector layer. I have a few ...
9
votes
5answers
11k views

How to join multiple records to single feature?

apologies for what I'm guessing is a really easy problem to solve. GIS user, not programmer here. I'm trying to create a join/relate in QGIS where I have a shapefile of buildings and to that I would ...
7
votes
2answers
3k views

QGIS display world country shape files centered on pacific ocean using Robinson, Miller Cylindrical or other projection

I wish to display a map in QGIS (world country shapefiles) showing all countries but centered on the Pacific area. I am not familiar with Proj4, so is there any way this can be done in QGIS please?
4
votes
2answers
472 views

Assign point IDs to respective start and end attributes of a polyline

I have two shapefiles, Point and Polyline. I'm trying to populate my polyline layer with the point data ID (systemID) where the lines start to where they end; eg. create two columns (from and to). The ...
9
votes
2answers
2k views

Why are heatmaps on qgis 2.8.1 produced in the wrong CRS?

I noticed that the heatmap calculation on the new upgrade version of qgis is given the raster map without any coordinate system. Have you got the same problem?

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