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GIS & Geospatial Data (QGIS, GeoPandas, PostGIS) Module 12

Professional practice interview questions

Interview questions on professional practice: short warm-ups, then what each harder question tests, the first step of a good answer and its follow-ups.

8 questions: 3 warm-ups and 5 with model answers · Levels: Fresher to senior

Warm-up questions

Short questions with short answers, each answered in full.

Fresher

What is lineage in metadata, and why does a user need it?

Answered in the lesson Data quality, metadata and reproducible workflows
Fresher to mid

Why compare geospatial results by shape rather than byte for byte?

Because file bytes change when libraries change, even when the data does not: a new GEOS may start a polygon at another vertex or add a vertex on a straight edge, and file writers change their defaults. Compare counts, areas and corners, within a tolerance, so tests fail on real changes only.
From the lesson Data quality, metadata and reproducible workflows
Fresher

What does a GIS analyst do that a geospatial developer usually does not, and the reverse?

Answered in the lesson GIS roles, portfolios and interview practice

Questions with model answers

What each question tests, the first step of a good answer and the follow-ups to expect.

Mid to senior

A district land-use report is rerun a year later on a new laptop, and 7 of 40 class areas differ from last year's published table, by up to 0.4 %. Nobody changed the code. How do you find the cause, and how do you make next year's run give the same numbers?
What it tests

Tracing differences to library versions and data, comparing results by meaning, and pinning an environment so a published analysis can be reproduced.

First step

Separate the three things that could have changed: the input data, the libraries, and the code's environment. Compare file checksums of the inputs, print the versions of GEOS, PROJ with its EPSG copy and GDAL in both environments, and check whether the areas were computed in the same CRS.
Follow-ups
- The inputs are identical and only PROJ differs. Which areas would move, and why?
- Last year's environment was never recorded. What can you still do?
- How do you publish the report so that this cannot happen again?
From the lesson Data quality, metadata and reproducible workflows
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In the answer:
- Model answer
- Follow-up answers
- Common mistakes
- Rubric
- Variants
- about 2 minutes
Fresher to mid

A partner sends a village boundary layer for a survey, with no metadata, three days before field work starts. What do you check before you use it, and what do you write down?
What it tests

Running quality checks by element, inferring and documenting what metadata is missing, and deciding whether data is fit for a purpose under time pressure.

First step

Ask the questions a metadata record would have answered: what the layer is, its CRS, where it came from, how accurate it is and what you may do with it. Meanwhile run checks by element: completeness against the list of villages, logical consistency of ids and rings, and the plausibility of its positions.
Follow-ups
- The layer has 412 villages and the list has 415. What next?
- How do you judge its positional accuracy without a survey of your own?
- What do you send back to the partner?
From the lesson Data quality, metadata and reproducible workflows
Model answer, Pro.
In the answer:
- Model answer
- Follow-up answers
- Common mistakes
- Rubric
- Variants
- about 2 minutes
Fresher to mid

You have built your skills in QGIS, GeoPandas and PostGIS, and the team you are interviewing with works in ArcGIS. The interviewer asks how quickly you could be useful. What do you say, and what do you show?
What it tests

Mapping concepts across tools honestly, naming the ideas behind the vocabulary, and planning how to close the gaps rather than hiding them.

First step

Translate before you answer: a feature class is a GeoPackage layer or a PostGIS table, a geodatabase a GeoPackage or a schema, ModelBuilder the QGIS model designer, a geoprocessing tool a Processing algorithm. Then pick one piece of your own work that shows each idea, so the answer is evidence rather than a promise.
Follow-ups
- Which ArcGIS skills would you still need to learn, and how?
- How would you show a workflow you built in QGIS to a team that uses ModelBuilder?
- What would you do in your first week?
From the lesson GIS roles, portfolios and interview practice
Model answer, Pro.
In the answer:
- Model answer
- Follow-up answers
- Common mistakes
- Rubric
- Variants
- about 2 minutes
Fresher to mid

"Walk me through one project in your portfolio." Answer it for a clinic coverage analysis of a town, in about two minutes, the way an interviewer would want to hear it.
What it tests

Telling a project as question, data, method, check and limits; using numbers; and showing judgement about what the result can and cannot say.

First step

Use the order of a good write-up: the question, the data and its licences, the method and why it was chosen, how the result was checked, its limits, and how someone could rerun it. Put one number in each part, so the interviewer hears evidence at every step.
Follow-ups
- What would you do differently with more time?
- How do you know the coverage figure is right?
- Who would use the result, and how?
From the lesson GIS roles, portfolios and interview practice
Model answer, Pro.
In the answer:
- Model answer
- Follow-up answers
- Common mistakes
- Rubric
- Variants
- about 2 minutes
Mid to senior

In a scenario round you are told: "Our dashboard's district totals of households differ from the state's report by up to 6 % in some districts. Work out why." How do you approach it, step by step, and what do you report back?
What it tests

Structuring a scenario answer: checks before conclusions, separating data, method and boundaries, and reporting findings with their uncertainty.

First step

Do not guess a cause; list the candidates and test each with one check: different boundary releases, households assigned by PIN code rather than by position, points near district lines, a name join that lost or swapped districts, and counting rules. Start with the largest differences and work down.
Follow-ups
- The boundaries are the same release. What next?
- How would you report a difference you cannot fully explain?
- How would you stop it from happening again?
From the lesson GIS roles, portfolios and interview practice
Model answer, Pro.
In the answer:
- Model answer
- Follow-up answers
- Common mistakes
- Rubric
- Variants
- about 2 minutes

All GIS & Geospatial Data (QGIS, GeoPandas, PostGIS) interview questions · The GIS & Geospatial Data (QGIS, GeoPandas, PostGIS) track

Warm-up questions

What is lineage in metadata, and why does a user need it?

Why compare geospatial results by shape rather than byte for byte?

What does a GIS analyst do that a geospatial developer usually does not, and the reverse?

Questions with model answers

A district land-use report is rerun a year later on a new laptop, and 7 of 40 class areas differ from last year's published table, by up to 0.4 %. Nobody changed the code. How do you find the cause, and how do you make next year's run give the same numbers?

A partner sends a village boundary layer for a survey, with no metadata, three days before field work starts. What do you check before you use it, and what do you write down?

You have built your skills in QGIS, GeoPandas and PostGIS, and the team you are interviewing with works in ArcGIS. The interviewer asks how quickly you could be useful. What do you say, and what do you show?

"Walk me through one project in your portfolio." Answer it for a clinic coverage analysis of a town, in about two minutes, the way an interviewer would want to hear it.

In a scenario round you are told: "Our dashboard's district totals of households differ from the state's report by up to 6 % in some districts. Work out why." How do you approach it, step by step, and what do you report back?