GIS & Geospatial Data (QGIS, GeoPandas, PostGIS) Module 9
Web maps interview questions
Interview questions on web maps: short warm-ups, then what each harder question tests, the first step of a good answer and its follow-ups.
Warm-up questions
Short questions with short answers, each answered in full.
-
Fresher
What do z, x and y mean in a tile address such as /14/11553/7334.png?
Answered in the lesson How web maps work: tiles and Web Mercator
Questions with model answers
What each question tests, the first step of a good answer and the follow-ups to expect.
-
Fresher to mid
A new tile server for a map of Pune shows only open sea from zoom 1 on, while the single tile at zoom 0 looks right. The tiles were cut with a command-line tiler and copied to the server as z/x/y files. What is wrong, how do you prove it, and how do you fix it?
- What it tests
- Knowing the XYZ and TMS row orders, reading a symptom that depends on the zoom, proving a guess with one known tile, and fixing it in the right place.
- First step
- Work out the tile that must hold central Pune at zoom 12, 12/2888/1833, and open it on the server. If it shows sea, compute the TMS row, 4,095 − 1,833 = 2,262, and open 12/2888/2262: if that tile shows Pune, the tiler wrote TMS rows and the map reads XYZ rows.
- Follow-ups
-
- Why did the zoom-0 tile look right?
- Do you rename the files, or change the map?
- How do you stop it from happening again?
From the lesson How web maps work: tiles and Web Mercator
Model answer, Pro. Model answers open with any pass; prices are in the notice on this page.Opening the model answers with your pass…
Model answers open with any MySmartCoPilot pass.
- Pro pass · 1 week₹79$2.99
- 30 days₹179$5.99
- 1 year₹1,699$45
One payment; a pass never renews. The price shown is the total you pay: no fees or charges are added at checkout.
Passes can’t be bought right now, so the model answers can’t be opened at the moment. If you have a pass, enter your licence key.
It also opens every other in-depth part in Learn and every Pro tool. Sales are final, except where the law gives you a right to withdraw, for example in the EU and the UK (refund policy).
In the answer:
- Model answer
- Follow-up answers
- Common mistakes
- Rubric
- Variants
- about 3 minutes
-
Mid to senior
A field app for 300 surveyors downloads every tile of the lesson's box around Pune, about 24 by 22 km, zooms 10 to 16, from tile.openstreetmap.org each morning, so that it works offline. Estimate the load, say what the tile policy says, and redesign the app's offline maps.
- What it tests
- Counting tiles across zooms, turning a design into daily requests, knowing the OpenStreetMap tile usage policy, and designing offline maps that respect the data's licence.
- First step
- Count the tiles first: the box needs 2 tiles at zoom 10 but 1,677 at zoom 16, 2,289 in all, so 300 devices make 686,700 requests every morning. Then read the policy: bulk downloading, prefetching and offline use are not allowed on those servers.
- Follow-ups
-
- What would you ship to each device instead?
- How often should the offline maps change?
- What credit must the offline map show?
From the lesson How web maps work: tiles and Web Mercator
Model answer, Pro.In the answer:
- Model answer
- Follow-up answers
- Common mistakes
- Rubric
- Variants
- about 3 minutes
All GIS & Geospatial Data (QGIS, GeoPandas, PostGIS) interview questions · The GIS & Geospatial Data (QGIS, GeoPandas, PostGIS) track